bar() (and possibly other plots) should take an array of string labels for x axis

[stevengj]

It's pretty common to have bar charts where the x axis is a set of string labels rather than numbers. This can currently be done in pyplot with e.g.

bar([1,2,3],[4,3,6], align='center')
gca().xaxis.set_ticks([1, 2, 3])
gca().xaxis.set_ticklabels(['one', 'two', 'three'])

but it would be much nicer to simply support

bar(['one', 'two', 'three'], [4,3,6])

Similarly for barh and possibly some other plot types.

cc: @alanedelman

[mdboom]

I think this is an interesting idea. It would be great to have a basic implementation as a starting point to see how best this could be handled and what APIs (if any) it might break.

[stevengj]

Since Axes.bar does not currently support arrays of strings for the first argument, this would be strictly new functionality and hence should not break any existing APIs.

My thinking was to simply add a few lines to bar() in _axes.py that do something like:

if all(isinstance(s, str) for s in left):
    labels = left
    left = range(1, len(left)+1)
    align = 'center'
else:
    labels = None

and then further below in the bar() function do something like

if labels != None:
    if orientation == 'horizontal':
        self.xaxis.set_ticks(left)
        self.xaxis.set_ticklabels(labels)
    else:
        self.yaxis.set_ticks(left)
        self.yaxis.set_ticklabels(labels)

(Though I'm not much of a Python hacker. I mainly use matplotlib from the Julia via the PyPlot.jl package.)

[ghost]

xticks can take care of the labeling problem associated with bar charts. see example below:

import matplotlib.pyplot as plt
x=[1,2,3,4]
labels=['jan','feb','mar','apr']
y=[40,70,30,54]
plt.bar(x,y, align='center')
plt.xticks(x, labels)

Output is shown below: