How to set a list as the index of an existing pandas dataframe?

Question

I have an existing pandas dataframe, which looks something like:

    Gr          R           B           Gb
0   1.537037    1.733333    1.400000    1.537037
1   1.657952    1.706522    1.650407    1.713024
2   1.670982    1.690476    1.626263    1.661202
3   1.689229    1.683761    1.607143    1.676923
...

I have a separate list, where the length of the list is equal to the number of rows in the above dataframe. Something like:

separate_list = ['a','b','c',....]

How can I make the separate list to be the index of the above dataframe, replacing the default index (0,1,2,…)? All I can find are ways to set an existing column to the index.

Thank you.

Asked By: wookiekim

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Source

Answer 1

Simply making your list a column of the DataFrame (df['new_index'] = separate_list) and then setting to be the index should work.

Answered By: Oliver.R

Answer 2

A pandas df has a set_index method that allows you to make an existing column or a separate series the new df index.

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.set_index.html

Answered By: Conner M.

Answer 3

Dataframe.set_index() will help you to do the same.
For your example, it will be,

DF = pd.DataFrame(#Your Dataframe)
DF.set_index(keys=separate_list)

Answered By: Rushabh Shah

Answer 4

Let DF be your pandas.DataFrame and index_list be a flat list with same size as DF rows, something like index_list = [0,1,2,3,4,5,6,...]:

DF.set_index(keys = [index_list])

will do it. And note that index_list must be enclosed between brackets in this case.

Alternatively, if index_list = [[0,1,2,3,4,5,6,...]] you should use:

DF.set_index(keys = index_list)

and now, there is no need to enclose it, that’s the way it goes with Shah’s example above.

Answered By: ePuntel

How to set a list as the index of an existing pandas dataframe?

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