Stacked bar plot by grouped data with pandas

Question

Let's assume I have pandas dataframe which has many features and I am interested in two. I'll call them feature1 and feature2 .

feature1 can have three possible values. feature2 can have two possible values.

I need bar plot grouped by feature1 and stacked by count of rows with each value of feature2 . (So that there will be three stacks each with two bars).

How to achieve this?

At the moment I have

import pandas as pd
df = pd.read_csv('data.csv')
df['feature1'][df['feature2'] == 0].value_counts().plot(kind='bar',label='0')
df['feature1'][df['feature2'] == 1].value_counts().plot(kind='bar',label='1')

but that is not what I actually want because it doesn't stack them.

Answer 1

Also, I have found another way to do this (with pandas):

df.groupby(['feature1', 'feature2']).size().unstack().plot(kind='bar', stacked=True)

Source: making a stacked barchart in pandas

Answer 2

Im not sure how to do this in matplotlib (pandas default plotting library), but if you are willing to try a different plotting library, it is quite easy to do it with Bokeh.

Here is an example

import pandas as pd
from bokeh.charts import Bar, output_file, show
x = pd.DataFrame({"gender": ["m","f","m","f","m","f"],
                  "enrolments": [500,20,100,342,54,47],
                  "class": ["comp-sci", "comp-sci",
                            "psych", "psych",
                            "history", "history"]})

bar = Bar(x, values='enrolments', label='class', stack='gender',
         title="Number of students enrolled per class",
         legend='top_right',bar_width=1.0)
output_file("myPlot.html")
show(bar)

Answer 3

size produces a column with a simple row count for that grouping, its what produces the values for the y axis. unstack produces the row and column information necessary for matplotlib to create the stacked bar graph.

Essentially it takes

>>> s
one  a   1.0
     b   2.0
two  a   3.0
     b   4.0

and produces:

>>> s.unstack(level=-1)
     a   b
one  1.0  2.0
two  3.0  4.0