CODEWITHSUNDEEP
pythonpandaspandas-groupby
Rylan Schaeffer
Rylan Schaeffer

Reputation: 2673

Pandas Groupby First - Extract Index from Original Dataframe

I have a very simple problem. I'd like to take a data frame, perform a groupby on some columns, and extract the index (in the original data frame) of the first row in each group. How do I do this?

I've tried playing with as_index, group_keys, reset_index() and nothing seems to work.

Upvotes: 1

Views: 368

Answers (1)

Minions
Minions

Reputation: 5477

You need the function first:

x = pd.DataFrame([{'name': 'b1', 'group': 'a'},
                  {'name': 'b2', 'group': 'a'},
                  {'name': 'b3', 'group': 'a'},
                  {'name': 'b4', 'group': 'b'},
                  {'name': 'b5', 'group': 'b'},
                  {'name': 'b6', 'group': 'a'},
                  {'name': 'b7', 'group': 'c'},
                  {'name': 'b8', 'group': 'c'},])
x = x.reset_index() # add the indices as a column
xc = x.groupby('group').first()
print(xc)


       index    name
group               
a          0  b1
b          3  b4
c          6  b7

Upvotes: 1

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