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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Modifying colormaps (as used in xarray)","articleBody":"`xarray`'s plotting functionality sometimes needs to turn a colormap into a discrete colormap. I came across this in fixing a bug https://github.com/pydata/xarray/pull/3601 where `xarray` was ignoring the effects of `set_under()`, etc., which had been called on the colormap. We've fixed that problem, but ended up with this https://github.com/pydata/xarray/blob/ae6609b025d62a0d863869cbd16db167a8855167/xarray/plot/utils.py#L94-L105\r\n```\r\n    n_colors = len(levels) + ext_n - 1\r\n    pal = _color_palette(cmap, n_colors)\r\n\r\n    new_cmap, cnorm = mpl.colors.from_levels_and_colors(levels, pal, extend=extend)\r\n    # copy the old cmap name, for easier testing\r\n    new_cmap.name = getattr(cmap, \"name\", cmap)\r\n\r\n    # copy colors to use for bad, under, and over values in case they have been set to\r\n    # non-default values\r\n    new_cmap._rgba_bad = getattr(cmap, \"_rgba_bad\", new_cmap._rgba_bad)\r\n    new_cmap._rgba_under = getattr(cmap, \"_rgba_under\", new_cmap._rgba_under)\r\n    new_cmap._rgba_over = getattr(cmap, \"_rgba_over\", new_cmap._rgba_over)\r\n```\r\nThis works, but is not particularly elegant, and if there are any other properties of the original `cmap` that we want to keep, we'd have to copy them over explicitly. @dcherian asked me to see if anyone on here could suggest a better way of modifying a `cmap` into a discrete `cmap`?","author":{"url":"https://github.com/johnomotani","@type":"Person","name":"johnomotani"},"datePublished":"2020-01-22T22:30:02.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":13},"url":"https://github.com/16296/matplotlib/issues/16296"}