Stacked bar plot from Dataframe using groupby

Question

I have the following dataframe and I am trying to create a stacked bar plot

import os
from pprint import pprint
import matplotlib.pyplot as plt
import pandas as pd


def classify_data():
    race = ['race1','race1','race1','race1','race2','race2','race2', 'race2']
    qualifier = ['last','first','first','first','last','last','first','first']
    participant = ['rat','rat','cat','cat','rat','dog','dog','dog']
    df = pd.DataFrame(
        {'race':race,
         'qualifier':qualifier,
         'participant':participant

        }
    )
    pprint(df)
    df2 = df.groupby(['race','qualifier'])['race'].count().unstack('qualifier').fillna(0)
    df2[['first','last']].plot(kind='bar', stacked=True)
    plt.show()



classify_data()

I could manage to obtain the following plot. But , I want to create two plots out of my dataframe

One plot containing the following data for the qualifier 'last'

Race1 rat 1
Race1 cat 0
Race1 dog 0 
Race2 rat 1
Race2 dog 1
Race2 cat 0

So the first bar plot would have 2 bars and each bar coded with a different color for the count of participant

Likewise a second plot for qualifier 'first'

EDIT:

  Race1 rat 1
  Race1 cat 2
  Race1 dog 0 
  Race2 rat 0
  Race2 dog 2
  Race2 cat 0

From the original dataframe , I have to create the above two dataframe for creating the stacked plots

I am not sure how to use the groupby function and get the count of 'participant' for each 'qualifier' for a given 'race'

EDIT 2 : For qualifier 'last' the desired plot would look like( blue for rat , red for dog).

For qualifier 'first'

Could someone suggest me on how to proceed from here?

@QuangHoang . No not for each column. For the qualifier , first and last, I want two separate stacked plots. So the first bar plot would have 2 bars and each bar coded with a different color for the count of participant — Natasha
– Natasha, Commented Jun 27, 2019 at 15:16
it's really hard to follow what you want to achieve, is there a way you can manually create the plots for clarity sake? — Yuca
– Yuca, Commented Jun 27, 2019 at 15:44

Quang Hoang · Accepted Answer · 2019-06-27 16:02:09Z

2

IIUC, this is what you want:

df2 = (df.groupby(['race','qualifier','participant'])
         .size()
         .unstack(level=-1)
         .reset_index()
      )

fig,axes = plt.subplots(1,2,figsize=(12,6),sharey=True)
for ax,q in zip(axes.ravel(),['first','last']):
    tmp_df = df2[df2.qualifier.eq(q)]
    tmp_df.plot.bar(x='race', ax=ax, stacked=True)

Output:

edited Jun 27, 2019 at 16:02

answered Jun 27, 2019 at 15:57

Quang Hoang

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12 Comments

Quang Hoang Over a year ago

@Natasha see edit for correct coloring of participants.

Natasha Over a year ago

Excellent! thanks a ton. Can this be plotted in plotly using df2?

Quang Hoang Over a year ago

Sorry, I'm not familiar with plotly.

Quang Hoang Over a year ago

If you want them all, you can replace ['first','last'] by, for example: df2.qualifier.unique(). But then you need to match the number of qualifiers with that of axes.

Quang Hoang Over a year ago

It's the same with .unstack('participant') (note that participant was last in the groupby list. I want participant to be columns so df.plot.bar will color them. Finally subplot title: ax.set_title().

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