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Getting the first row of each group in Pandas

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Data Aggregation Cookbook
schedule Jul 1, 2022
Last updated
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To get the first row of each group, call first() after grouping.

Example

Consider the following DataFrame:

df = pd.DataFrame({"price":[200,300,700,900], "brand":["apple", "google", "apple", "google"], "device":["phone","phone","computer","phone"]})
df
price brand device
0 200 apple phone
1 300 google phone
2 700 apple computer
3 900 google phone

To get the first row of each brand group:

df.groupby("brand").first()
price device
brand
apple 200 phone
google 300 phone

Note that groupby(~) method preserves the ordering of the rows, and so it is guaranteed to get the first occurrence of each brand in this case.

* * *

As a side note, you could also fetch the first n rows of each group using the head(~) method:

df.groupby("brand").head(2)
price brand device
0 200 apple phone
1 300 google phone
2 700 apple computer
3 900 google phone
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Published by Isshin Inada
Edited by 0 others
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