Select single row with DataFrame.loc[] without index

Question

Assuming I have a DataFrame:

import pandas as pd
df = pd.DataFrame([["house", "red"], ["car", "blue"]], columns=["item", "colour"])

What is the idiomatic way to return a single row, or raise an exception if exactly one row is not found, using DataFrame.loc:

match = df.loc[df["colour"] == "red"]]
# I know there is exactly one row in the resulting DataFrame
# TODO: How to make match to return a single row as pd.Series

This would be similar to SQLAlchemy's Query.one()

mozway · Accepted Answer · 2022-08-11 20:16:51Z

2

You can squeeze and assert that the output is a Series (or use a test if you don't want to raise an exception):

match = df.loc[df["colour"] == "red"].squeeze()

assert isinstance(match, pd.Series)

alternative to assert:

if isinstance(match, pd.Series):
    # do something
else:
    # do something else

answered Aug 11, 2022 at 20:16

mozway

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