Implement a relative reference robust to source and reference moving
The new function is X(SRC,REF), which briefly for a cell in the neighborhood of REF returns the corresponding cell in the neighborhood in SRC. For further details, see the updated documention. In developing and documenting this function, I refined some of the existing error messages (e.g. showing the coordinates when there is an attempt to obtain a cell with a negative coordinate) and improved the error propagation to increase the chance that the innermost error will percolate to the top level.
This commit is contained in:
Glen Whitney
parent
ab1a2fbb5a
commit
341b12ba04
12 changed files with 650 additions and 238 deletions
421
doc/teapot.lyx
421
doc/teapot.lyx
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@ -4625,7 +4625,7 @@ save-tbl
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file
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\series default
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\emph default
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\end_layout
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\begin_layout Description
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@ -4642,7 +4642,7 @@ save-csv
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file
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\series default
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\emph default
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\end_layout
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\begin_layout Description
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@ -4659,7 +4659,7 @@ save-latex
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file
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\series default
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\emph default
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\end_layout
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\begin_layout Description
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@ -4676,7 +4676,7 @@ save-context
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file
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\series default
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\emph default
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\end_layout
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\begin_layout Description
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@ -4855,6 +4855,11 @@ Location Cell labels and the
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&()
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\family default
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function have this type, but there are no location constant literals.
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However,
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\family typewriter
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&(3,2,1),
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\family default
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for example, acts very much like a location constant literal.
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\end_layout
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\begin_layout Description
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@ -5041,7 +5046,7 @@ y
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x
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\family typewriter
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\emph default
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=
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~=
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\family default
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\emph on
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y
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@ -5489,7 +5494,8 @@ y
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z
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\emph default
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is omitted, the coordinate of the cell is used.
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The second form is in fact a no-op, but it is allowed for convenience
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The second form is in fact a no-op, but it is allowed for convenience and
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consistency of expressions.
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\end_layout
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\begin_layout Description
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@ -5515,8 +5521,21 @@ relative.
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\begin_inset Quotes erd
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\end_inset
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Thus R(-1) returns the value of the cell immediately to the left of this
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one.
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Thus
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\family sans
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\series bold
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R
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\series default
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(-1)
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\family default
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returns the value of the cell immediately to the left of this one, and
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\family sans
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\series bold
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R
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\series default
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(,,1)
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\family default
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returns the same cell as this one but on the following layer.
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\end_layout
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\begin_layout Description
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@ -5541,8 +5560,181 @@ displaced (by).
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\begin_inset Quotes erd
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\end_inset
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Thus, D(-1) returns the location of the cell immediately to the left of
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this one.
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Thus,
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\family sans
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\series bold
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D
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\series default
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(-1)
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\family default
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returns the location of the cell immediately to the left of this one, and
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\family sans
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\series bold
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D
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\series default
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(,2,1)
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\family default
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returns the location of the cell two below this one on the following layer.
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\end_layout
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\begin_layout Description
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X(
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\series medium
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label
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\emph on
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\begin_inset space ~
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\end_inset
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to,
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\begin_inset space ~
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\end_inset
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\emph default
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label
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\emph on
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\begin_inset space ~
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\end_inset
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from,
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\begin_inset space ~
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\end_inset
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\emph default
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[bool
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\emph on
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\begin_inset space ~
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\end_inset
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fix_x
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\emph default
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]
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\emph on
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,
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\begin_inset space ~
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\end_inset
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\emph default
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[bool
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\emph on
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\begin_inset space ~
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\end_inset
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fix_y
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\emph default
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]
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\emph on
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,
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\begin_inset space ~
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\end_inset
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\emph default
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[bool
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\emph on
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\begin_inset space ~
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\end_inset
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fix_z
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\emph default
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]
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\series default
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)
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\begin_inset Quotes eld
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\end_inset
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Excel reference
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\begin_inset Quotes erd
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\end_inset
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: returns the value of the cell at a computed target location.
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This target location is the one reached from the current cell via the same
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offset as the cell with label
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\emph on
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to
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\emph default
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has from label
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\emph on
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from.
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\emph default
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The idea is that if you label the source of data you want to reference,
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say with
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\family sans
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SRC
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\family default
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, and the location of some place you want to start referring to it with
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\family sans
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REF
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\family default
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, then you can use
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\family sans
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\series bold
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X
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\series default
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(SRC,REF)
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\family default
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to refer to the source data, and fill this formula to neighboring cells
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to refer to the neighbors of the source, and it will all continue to work
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if either the source or the reference is moved around in the sheet.
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\begin_inset Newline newline
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\end_inset
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If the
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\emph on
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fix_DIM
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\emph default
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argument is present and positive, then the corresponding coordinate of
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the target cell is set to match that of
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\emph on
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to
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\emph default
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.
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This corresponds to fixing the row or column (or layer) of the reference,
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as with a
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\begin_inset Quotes eld
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\end_inset
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$
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\begin_inset Quotes erd
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\end_inset
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character in Excel.
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Thus
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\family sans
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\series bold
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X
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\series default
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(SRC,REF,1,1,1)
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\family default
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is identical to
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\family sans
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@(SRC)
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\family default
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, but you should certainly prefer the latter for clarity of expression.
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\begin_inset Newline newline
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\end_inset
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There is a corresponding location function
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\family sans
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X&()
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\family default
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as well, which takes exactly the same arguments with the same meanings,
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but it is rarely needed.
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It is provided for completeness.
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\begin_inset Newline newline
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\end_inset
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See the FAQ below for further discussion of cell references.
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\end_layout
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\begin_layout Description
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@ -5904,7 +6096,7 @@ clock
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condition
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\emph default
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,[location[,location])
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,[location[,location])
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\series default
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conditionally clocks the specified cell if the condition is not 0.
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If two locations are given, all cells in that range will be clocked.
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@ -7264,8 +7456,22 @@ z
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position of the given location, of the currently updated cell if none is
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given.
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These functions are usually used in combination with the @ function for
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relative relations to other cells.
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relative relations to other cell, but see also the convenience functions
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\family sans
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\series bold
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R
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\series default
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()
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\family default
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and
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\family sans
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\series bold
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D
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\series default
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()
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\family default
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for relative references.
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\end_layout
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\begin_layout Subsection
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@ -7763,11 +7969,13 @@ X
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\end_layout
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\begin_layout Quote
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eval(&((@(X)>=0)+x(BAD),y(BAD),z(BAD)))
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eval(BAD + &((@(X)>=0),0,0))
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\end_layout
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\begin_layout Standard
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The cell labelled
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Note this is making use of the fact that you can add locations in the natural
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way.
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The cell labelled
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\family typewriter
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BAD
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\family default
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@ -7786,5 +7994,190 @@ BAD
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\end_layout
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\begin_layout Subsection
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But my references don't do the right thing when I move or copy them!
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\end_layout
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\begin_layout Standard
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If you are used to other spreadsheets, you have probably noticed that references
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like
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\family sans
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@(0,1,0)
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\family default
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(for the start of the second row) or
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\family sans
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@(MYDATA)
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\family default
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(for a location) are
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\begin_inset Quotes eld
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\end_inset
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absolute
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\begin_inset Quotes erd
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\end_inset
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– they always refer to the same location no matter where in the spreadsheet
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they occur.
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And of course sometimes it is convenient, for example when making a column
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of consecutive numbers, to refer to nearby cells in a relative manner,
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either with say
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\family sans
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@(x(),y()-1,z())+1
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\family default
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or
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\family sans
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@(&()+&(0,-1,0))+1
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\family default
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or just
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\family sans
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R(,-1)+1
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\family default
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to add one to the value of the cell just above.
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Then you can fill that expression down and get your column of consecutive
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numbers.
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\end_layout
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\begin_layout Standard
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But these sorts of relative expressions only keep working if the cells move
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together with the cells they refer to.
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If for example you have a row of cells that are all referring to the row
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above with a relative reference (like
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\family sans
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R(,-1)
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\family default
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) and you insert another row in between them, your references will be all
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messed up.
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There is value to
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\begin_inset Quotes eld
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\end_inset
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Excel-style
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\begin_inset Quotes erd
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\end_inset
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references that can be used to fill and which also can move around while
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still just
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\begin_inset Quotes eld
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\end_inset
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referring to what you want.
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\begin_inset Quotes erd
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\end_inset
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\end_layout
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\begin_layout Standard
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To provide for this need, teapot has a function
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\family sans
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X(SRC, REF)
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\family default
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to retrieve the value of the cell labeled
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\family sans
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SRC
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\family default
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\bar under
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from
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\bar default
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the cell labeled
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\family sans
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REF
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\family default
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.
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If the so-labeled cells move around (either the source or the reference)
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it will still work.
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This is not particularly useful in and of itself; what makes it useful
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is that from a cell other than
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\family sans
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REF
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\family default
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, it gives you the value of the cell that stands in the same relation to
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\family sans
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SRC
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\family default
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as that cell stands to
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\family sans
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REF
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\family default
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.
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So in the cell to the right of
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\family sans
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REF
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\family default
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, it will give you the value of the cell to the right of
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\family sans
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SRC
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\family default
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; in the cell below, it gives you the cell below
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\family sans
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SRC
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\family default
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, etc.
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Now you can fill a block of cells around
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\family sans
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REF
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\family default
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with formulas contaning
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\family sans
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X(SRC,REF)
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\family default
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and they will refer to the analogous block of cells around
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\family sans
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SRC
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\family default
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.
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\end_layout
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\begin_layout Standard
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Sometimes you want to make this kind of reference but fix one of the coordinates
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but not the others;
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\family sans
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X()
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\family default
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has optional flags for this, as well, so that
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\family sans
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X(SRC,REF,,,1)
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\family default
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will always be on the same layer as
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\family sans
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SRC
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\family default
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regardless of what layer it is called from or what layer
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\family sans
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REF
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\family default
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is on.
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Thus
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\family sans
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X(SRC,REF,1,1,1)
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\family default
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is just
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\family sans
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@(SRC)
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\family default
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, but the intent of the latter is much clearer.
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\end_layout
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\begin_layout Standard
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You might ask as a follow-up question: Isnt
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\family sans
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X(SRC, REF)
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\family default
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much more cumbersome than just referring to cells by coordinate and then
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letting Excel just do the right thing as you copy and move either that
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formula or the referred-to data? The response to this is that in a typical
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spreadsheet, there are only a small number of fundamental references, and
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all other references derive from them in this way.
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So you generally only need a few labels, and by taking just a little extra
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time to apply those labels and refer to them in initial formulas, you are
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making the semantics of your references much clearer and in essence documenting
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them within your spreadsheet.
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This extra effort will therefore be repaid in an easier-to-use, easier-to-under
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stand, and easier-to-maintain and update spreadsheet.
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\end_layout
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\end_body
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\end_document
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|
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Loading…
Add table
Add a link
Reference in a new issue