Lo-Fi Python

Create a Column of Values in Pandas with df.assign()

Pandas is amazing, what else is there to say? Learning the nuances of its API have yielded tons of times where it helped me get stuff done.

I recently picked up the pandas dataframe's "assign" function for creating a new column of values. This is an elegant way to set a column of values in tabular data with the pandas library. Below you'll see two ways to set a column of values in pandas. In the first way, I am chaining two assign functions together to create 2 new columns, "sound" and "type". I prefer using assign because it looks better and it does not result in any warnings from pandas. Highly recommend getting familiar with pandas functions like assign and API nuances like Series accessors to up your tabular data game.

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import pandas as pd
cats = ["Garfield","Meowth","Tom"]
df = pd.DataFrame([cats], columns=["cats"])
# best way
df = df.assign(sound="Meow").assign(type="Cartoon")
print(df.head())

# alternative way that also works, but with warnings from pandas
# df["sound"] = "Meow"

DataFrame.assign : Can evaluate an expression or function to create new values for a column. pandas source code: https://github.com/pandas-dev/pandas/blob/v1.3.5/pandas/core/frame.py#L4421-L4487