How to add legends and title to grouped histograms generated by Pandas

Question

I am trying to plot a histogram of multiple attributes grouped by another attributes, all of them in a dataframe.

with the help of this question, I am able to set title

Answer 1

You can almost get what you want by doing:

g.plot(kind='bar')

but it produces one plot per group (and doesn't name the plots after the groups so it's a bit useless IMO.)

Here's something which looks rather beautiful, but does involve quite a lot of "manual" matplotlib work, which everyone wants to avoid, but no one can:

import numpy.random as rnd
import pandas as pd
import matplotlib.pyplot as plt
from matplotlib import cm

x = pd.DataFrame(rnd.randn(100).reshape(20, 5), columns=list('abcde'))

group_col = 'groups'
groups = ['foo', 'bar', 'baz']
x[group_col] = pd.Series(rnd.choice(groups, len(x)))

g = x.groupby(group_col)
num_groups = g.ngroups

fig, axes = plt.subplots(num_groups)
for i, (k, group) in enumerate(g):
    ax = axes[i]
    ax.set_title(k)
    group = group[[c for c in group.columns if c != group_col]]
    num_columns = len(group.columns)
    colours = cm.Spectral([float(x) / num_columns for x in range(num_columns)])
    ax.hist(group.values, 5, histtype='bar',
            label=list(group.columns), color=colours,
            linewidth=1, edgecolor='white')
    ax.legend()

plt.show()

Which I think gives you what you want:

---

Update In response to comments (and as this answer is a few years old) I've tried to strip this answer down to its barest bones. There may now be a way of labelling plots of groupby objects but I don't know of it.

Here's the simplest possible way to do this:

axes = g.plot(kind='hist')
for i, (groupname, group) in enumerate(g):
    axes[i].set_title(groupname)