Legend or Key for charts with colored groups

[Michael Wayne Goodman]

When I make a bar chart, I like the ability to compare different sources of data with groups. For example, here is a chart I'm using for:

cairoplot.vertical_bar_plot('barchart.png',
  [ [0.87, 0.82], [0.83, 0.50], [0.70, 0.11] ],
  340, 280, border = 10, grid = True,
  x_labels = ['Parses', 'Generates', 'Generates Original'],
  y_labels = ['%d%%' % i for i in range(0,110,10)],
  y_bounds = (0,1) )

I've attached the png file generated so you can see what I mean.

Which makes a nice bar chart with three groups with two bars each. I can label the groups (as I have done here), but I cannot label what each color means. I would like to have a legend on some side of the chart with each color in a box and a label next to it. This could be defined as:

legend = ['Grammar 1', 'Grammar 2']

where 'Grammar 1' (yellow) is the source for the 0.87, 0.83, and 0.70 in the data, and 'Grammar 2' (blue) is for the 0.82, 0.50, and 0.11.

[Rodrigo Moreira Araújo (alf-rodrigo)]

Nice observation.
I don't know you've seen but the ScatterPlot, DotLinePlot and FunctionPlot classes already support that. Whenever a user passes data using dictionaries, the dictionaries keys are plotted on a little box on the upper corner.

For BarPlot charts it won't be possible to use dictionaries. I'll give it further studying though. If I don't find a way to maintain code compatibility, I believe I'll follow your advice and add a new parameter to the function. Something like group_legend or group_names.

[Michael Wayne Goodman (goodmami)]

I would suggest not calling it "group_(something)" because "group" is already used in reference to those bars that are next to each other (eg. [0.87, 0.82] in the example above), although that terminology might only be used in the documentation and examples rather than code. Perhaps "data source" is more descriptive? Alternatively, call it a "group", but then find a different word for what was a "group" before, like "comparison" or something.

[Rodrigo Moreira Araújo (alf-rodrigo)]

Committed a partial solution on revision 32.
Through the parameter series_labels (this name was selected to maintain the relation with the ScatterPlot) the user might pass a list of strings. These will be plotted on a box on the right upper corner of the image displaying which color represents each of the strings.
It's still partial because the user cannot define the plotting position of the box.

[Rodrigo Moreira Araújo (alf-rodrigo)]

My mistake, the partial solution was committed on revision 33.