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docs: document variable color assignment for histogram components · gnuplot/gnuplot@09ef613 · GitHub

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Commit 09ef613

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Ethan A Merritt
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docs: document variable color assignment for histogram components
Add a section to the user manual. Add a corresponding example histogram_colors.dem to the demo collection.
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‎demo/all.dem‎

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@@ -398,6 +398,7 @@ load "histograms.dem"
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load "histograms2.dem"
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load "histerror.dem"
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load "label_stacked_histograms.dem"
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load "histogram_colors.dem"
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reset
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print "********************** file boxclusters.dem *********************"

‎demo/histogram_colors.dem‎

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#
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# Show how variable color can be used to histogram categorical data even
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# when the data sources are not completely parallel. Each data file
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# (datablock in this demo) contains a column with a category identifier
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# and a column with the data value contributing to the histogram.
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# However not all categories are present in each file, so they are not
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# parallel in that the Nth line of two files may or may not belong to
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# the same category.
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# Therefore gnuplot's automatic color assignment would fail.
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# Instead we use the category identifier to assign colors.
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#
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$Set1 << EOD
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A 15
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B 21
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C 12
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D 9
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G 15
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L 12
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EOD
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$Set2 << EOD
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B 14
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C 12
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D 16
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E 8
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G 14
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H 19
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I 20
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EOD
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$Set3 << EOD
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D 13
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E 7
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F 14
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G 11
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H 15
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I 4
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L 11
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EOD
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unset border
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set tics nomirror
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unset ytics
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set boxwidth 0.8
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set key lmargin maxcol 1 invert
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set key title " Category "
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# Set up a range of 12 defined linetype colors
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set for [i=1:8] linetype 100+i lc i # copy the default 8 colors
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set linetype 109 lc "gray50" # then add a few more
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set linetype 110 lc "white"
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set linetype 111 lc "orchid"
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set linetype 112 lc "seagreen"
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alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
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color(category) = 100 + strstrt(alphabet, category)
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set style data histogram
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set style histogram columns
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set style fill solid border lc "black"
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set title "Column-stacked histogram colored by data category"
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plot for [data in "$Set1 $Set2 $Set3"] \
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data using 2:(color(strcol(1))) lc variable title data, \
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for [i=1:12] keyentry with boxes lc color(alphabet[i:i]) title alphabet[i:i]
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pause -1 "<cr> to continue"
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reset

‎docs/gnuplot.doc‎

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#b Change: Text rotation angle is not limited to integral degrees.
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#b Special (non-numerical) linetypes `lt nodraw`, `lt black`, `lt bgnd`
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## See `special_linetypes`.
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#b Data-driven color assignments in histogram plots. See `histograms colors`.
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#end
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3 Features introduced in version 5.4
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corresponding to the second entry in the respective data columns, and so on.
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The default gap width of 2 indicates that the empty space between clusters is
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equivalent to the width of 2 boxes. All boxes derived from any one column
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are given the same fill color and/or pattern (see `set style fill`).
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are given the same fill color and/or pattern; however see the subsection
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`histograms colors`.
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Each cluster of boxes is derived from a single row of the input data file.
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It is common in such input files that the first element of each row is a
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The `columnstacked` style is similar, except that each stack of boxes is
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built up from a single data column. Each data value from the first specified
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column yields a box in the stack at x=1, each data value from the second
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specified column yields a box in the stack at x=2, and so on. In this style
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the color of each box is taken from the row number, rather than the column
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number, of the corresponding data field.
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data column yields a box in the stack at x=1, each data value from the second
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specified data column yields a box in the stack at x=2, and so on.
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In this style the color of each box is taken from the row number, rather than
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the column number, of the corresponding data field.
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Box widths may be modified using the `set boxwidth` command.
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Box fill styles may be set using the `set style fill` command.
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set style histogram columnstacked
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plot for [i=3:8] "datafile" using i title columnhead
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3 histogram color assignments
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?with histograms colors
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?histograms colors
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The program assigns a color to each component box in a histogram
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automatically such that equivalent data values maintain a consistent
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color wherever they appear in the rows or columns of the histogram.
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The colors are taken from successive linetypes, starting either with
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the next unused linetype or an initial linetype provided in a
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`newhistogram` element.
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In some cases this mechanism fails due to data sources that are not
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truly parallel (i.e. some files contain incomplete data). In other
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cases there may be additional properties of the data that could be
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visualized by, say, varying the intensity or saturation of their base
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color. As an alternative to the automatic color assigmnent, you can
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provide an explicit color value for each data value in a second `using`
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column via the `linecolor variable` or `rgb variable` mechanism.
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See `colorspec`. Depending on the layout of your data, the color category
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might correspond to a row header or a column header or a data column.
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Note that you will probably have to customize the key sample colors
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to match (see `keyentry`).
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Example: Suppose file_001.dat through file_008.dat contain one column with
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a category identifier A, B, C, ... and a second column with a data value.
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Not all of the files contain a line for every category, so they are not
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truly parallel. The program would be wrong to assign the same color to the
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value from line N in each file. Instead we assign a color based on the
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category in column 1.
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file(i) = sprintf("data_%03d.dat",i)
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array Category = ["A", "B", "C", "D", "E", "F"]
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color(c) = index(Category, strcol(c))
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set style data histogram
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plot for [i=1:8] file(i) using 2:(color(1)) linecolor variable
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A more complete example including generation of a custom key is in the
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demo collection
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^ <a href="http://www.gnuplot.info/demo/histogram_colors.html">
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histogram_colors.dem
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^ </a>
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2 image
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?plotting styles image
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?style image
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2 columns: x y # line from [x,0] to [x,y] (2D)
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3 columns: x y z # line from [x,y,0] to [x,y,z] (3D)
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#TeX \newpage
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2 labels
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?plotting styles labels
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?style labels
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plot $Data using 1:2:3:4:5 with labels tc variable rotate variable
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#TeX \newpage
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2 lines
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?plotting styles lines
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?style lines

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