A graph's data can now hold blank cells: an empty CSV cell, a null in
`rows` (any cell that isn't a finite number), the rest of a short row,
or a row that has only a label.
- Columns, bars and stacked segments leave a blank cell out instead of
drawing a zero-height mark.
- Line and scatter graphs break their lines around it and draw no
marker there; the value axis ignores it.
- Area, pie and radar graphs draw it as 0, which is what it adds to
them.
The help pages don't describe blank cells, so this is our own choice:
a cell with no value has nothing to draw, which also matches how a
series with a missing year reads in a report.
In the file a blank cell keeps a 0 in `rows` and is listed in a new
`blanks` field ([category, series] pairs, written only when there are
any). A version that doesn't know blanks ignores the field and reads
the zeros, so files still open there, and files without blanks are
unchanged.
A number in straight quotes is a label, as the help page on graph
labels says (a year as a category name, for one). The CSV reader used
to strip the quotes first and read it as a value. Label columns are now
decided for the whole column: once any row starts with a label, every
row's first cell is its label, so a row with an empty label no longer
shifts its values one place left. The data window writes a header row,
labels that are empty, read as numbers or have spaces around them in
quotes, and blanks as empty cells, so they come back as they were.
graph.setData {} returns blanks in `rows` as null, so the rows it
returns can be edited and sent back. A label-only row keeps its place
with blank values; a row with neither a value nor a label is dropped,
and a first row that is a label followed by empty cells (`Year,,`) is
still read as a header with no series names.
The data grid is built in full for drawing and for the data window, so
it now stops at 10,000 categories of 256 series, which keeps a file
with one very long row from allocating without bound.
Behaviour (quoted labels): Add graph labels and data sets:
https://helpx.adobe.com/illustrator/desktop/automate-visualize-data/visualize-data/add-graph-labels-and-data-sets.html
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