How to create a stacked bar for each group

Question

I have the following dataset:

SessionId    Query
   1           a   
   1           b
   2           a
   3           b
   3           b
   3           c
   3           a

I want to display a stacked bar chart where there will be a bar for each Session and the bar will consist of different colors for each Query that it has, the stacked size will be in the size of the number of queries in each session.

I tried something like this:

result = data.groupby('SessionId').apply(
   lambda group: (
      group.groupby('Query').apply(
         lambda queryGroup: (
            queryGroup.count()
         )                
      )
   )
 )

But it gives a weird table inside a table

Asked By: Lee

||

Source

Answer 1

Pandas stacked bar chart relies on plotting different columns, so you’d need to pivot your data table to get the queries as columns holding the number of queries in rows.

Try this:

df = pd.DataFrame({"session":[1,1,2,2,3,3],
              "query":list("ababab"), "count":[5,7,32,5,8,1]})
df.pivot("session","query").plot(kind="bar", stacked=True)

Output:

Answered By: Nils Gudat

Answer 2

crosstab should do the job if I understand your question correctly:

import pandas as pd

data = pd.DataFrame({'SessionId': [1, 1, 2, 3, 3, 3, 3], 
                     'Query': ['a', 'b', 'a', 'b', 'b', 'c', 'a']})

pd.crosstab(data.SessionId, data.Query).plot.barh(stacked=True)

Answered By: stephan

How to create a stacked bar for each group

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