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Expanding lists vertically in a DataFrame in Pandas

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Data Manipulation Cookbook
schedule Jul 1, 2022
Last updated
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To expand lists vertically in a Pandas DataFrame, use the DataFrame's explode(~) method.

Example

Consider the following DataFrame:

df = pd.DataFrame({"A":[["a","b"], [],"c"],"B":[4,5,6]})
df
A B
0 [a,b] 4
1 [] 5
2 c 6

To vertically expand the lists so that each item in the lists get their own row:

df.explode("A")
A B
0 a 4
0 b 4
1 NaN 5
2 c 6

Note the following:

  • the index 0 was duplicated since its list contains two values (["a","b"])

  • the [] list was converted into NaN.

If you want non-duplicate index values, call reset_index(~), which will reset the index to the default integer index:

df.explode("A").reset_index(drop=True)
A B
0 a 4
1 b 4
2 NaN 5
3 c 6

Here, the drop=True is needed - otherwise the current index will be appended as a column.

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Published by Isshin Inada
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