Incomplete Legends

[zachcp]

Legends do not always contain all of the members in the legend. Here is an example with built in data where there should be 32 although only eight get plotted. I've tried a couple of examples and the legend seems to max out at eight. Most use cases won't need 32 but I often have more than eight items in a legend.

from ggplot import *
ggplot(aes(x= 'cyl', y='mpg', colour='name'), data=mtcars) + geom_point()

[jankatins]

Thats suspiciously the same number as there are colors defined. Current HEAD lets you set more than 8 colors via ggplot(...) + scale_colour_manual(values=color_list), where color_list is a list of html encoded colors ['#12AB34',...].

If that works, this should probably be fixed by throwing an error when the last color is used in color_gen() (source) and using a palette which has more colors (not sure how...)

[zachcp]

@JanSchulz Good catch. Thats exactly what it was. If you add 32 color to color_list it plots correctly (although 32 is too many items for the legend, especially since the legend does not wrap in any way).

The simple fix, as you say, is to make a default color pallete with more colors. Because the generators are called later in the ggplot.py file, i think the only solution is to make the color_list longer or to allow the color_gen function to sample an arbitrarily large color space.

How does the original ggplot do this? They have a consistent color scheme but I don't know how its mapped.

[jankatins]

They know the number of items and then ask a function in the scale package for the number of colors. This would mean that the current implementation needs to change, as currently color generator does not know the number of values it needs to generate. I will have a look...

[zachcp]

In ggplot.py the number of uniques are already calculated on line 325 with possible_colors = np.unique(mapping.color). I vote for completely replacing thecol_gen function with color generator that can accept an arbitrary number of values. Let me know if you want me to work on this.

[glamp]

Yeah this sounds good. I believe it has already been merged.

[jankatins]

Nope: the problem is in https://github.com/yhat/ggplot/blob/master/ggplot/components/colors.py -> it recyles the last color, but the code is doing a reverse coding https://github.com/yhat/ggplot/blob/master/ggplot/ggplot.py#L340 which results that the second round color -> Value overwrites the first round color -> Value pair.

The fix is to a) precompute the number of colors needed and b) use a color generator which can give an arbitrary number of colors (that's what ggplot2 does)
OR
don't cycle to colors but throw an error if another color is requested and give a helpful error message how to set more colors.

I suspect that both variants are need for the case when you manually specify colors but they are not enough for the given values.

[glamp]

fixed in 0.9.3