Filtering, groupby and merge

Split, summarise, and join two tables without silently losing rows.

13 min read · Lesson 4 of 6 · Pro

The dataset for this lesson

Python 3

import pandas as pd

df = pd.DataFrame({
    "roll":   [101, 102, 103, 104, 105, 106],
    "name":   ["Ravi", "Sneha", "Arjun", "Meera", "Imran", "Divya"],
    "branch": ["CSE", "CSE", "ECE", "ECE", "MECH", "CSE"],
    "sem":    [3, 3, 5, 5, 3, 5],
    "marks":  [78, 92, 55, 88, 41, 67],
})

groupby is split, apply, combine

Three steps every time:

Split the rows into groups by some column.
Apply a function to each group.
Combine the answers into one result.

Python 3

print(df.groupby("branch")["marks"].mean())

Code

branch
CSE     79.000000
ECE     71.500000
MECH    41.000000

More than one statistic at a time:

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