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pythonmatplotlibcolorbar

Generating just a colorbar with labels

I'm trying to generate just a colorbar in matplotlib to go with a series of clustermaps, following this guide.

Here is my current code:

fig, ax = plt.subplots(figsize=(3,8))
cmap = mpl.cm.inferno
bounds = [0,1,2,3,4,5]
norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
fig.colorbar(
    mpl.cm.ScalarMappable(cmap=cmap, norm=norm),
    ticks=[0.5,1.5,2.5,3.5,4.5],
    # labels=["A", "B", "C", "D", "E"],
    cax=ax)

But I would like to add labels to each of the ticks. How do I do this? colorbar() doesn't recognise any label-style arguments.

This problem is different to those answered here or here: I am generating just a colorbar, and so using methods like fig.colorbar.set_ticklabels() do not work. I have tried

mycb = fig.colorbar(
    mpl.cm.ScalarMappable(cmap=cmap, norm=norm),
    ticks=[0.5,1.5,2.5,3.5,4.5],
    cax=ax)

## opt 1
mycb.set_ticklabels = ["A", "B", "C", "D", "E"]

## opt2
mycb.ax.set_yticklabels = ["A", "B", "C", "D", "E"]

And neither produce labels on the ticks of my colorbar.

Solution

  • As docs for Colorbar class tell us, Colorbar can take a Formatter as one of the arguments (namely, format). The Formatter that takes a sequence of labels is called FixedFormatter, so this code would suffice:

    from matplotlib.ticker import FixedFormatter
mycb = fig.colorbar(
    mpl.cm.ScalarMappable(cmap=cmap, norm=norm),
    ticks=[0.5,1.5,2.5,3.5,4.5],
    format=FixedFormatter(['A', 'B', 'C', 'D', 'E']),
    cax=ax)

    The result is shown below:

    The colorbar with labels