问题
Pandas DataFrame has a rename method which takes a parameter named "index." I don't understand the description of the parameter in the documentation: DataFrame.rename
Specifically, I'm using it like the example on the documentation web page:
df.rename(index=str, columns={"A": "a", "B": "c"})
I understand the result, but I don't understand why we set index=str.
What is the index parameter used for?
Why does the example set index=str?
回答1:
The index parameter is used to rename index, take df from the example:
df.index
# RangeIndex(start=0, stop=3, step=1)
df.rename(index=str).index # converts index from int to str
# Index(['0', '1', '2'], dtype='object')
This works because in the rename function, you can also pass functions to index and columns parameter which will be applied to each element in the index and columns. Here str acts as a function and convert every index from int to str object.
Another example:
df.rename(index=lambda x: x*2).index
# Int64Index([0, 2, 4], dtype='int64')
来源：https://stackoverflow.com/questions/42080360/what-is-the-parameter-index-in-pandas-dataframe-rename-method