How to apply “first” and “last” functions to columns while using group by in pandas?

Question

I have a data frame and I would like to group it by a particular column (or, in other words, by values from a particular column). I can do it in the following way: gro

Answer 1

I would use a custom aggregator as shown below.

d = pd.DataFrame([[1,"man"], [1, "woman"], [1, "girl"], [2,"man"], [2, "woman"]],columns = 'number family'.split())
d

Here is the output:

    number family
 0       1    man
 1       1  woman
 2       1   girl
 3       2    man
 4       2  woman

Now the Aggregation taking first and last elements.

d.groupby(by = "number").agg(firstFamily= ('family', lambda x: list(x)[0]), lastFamily =('family', lambda x: list(x)[-1]))

The output of this aggregation is shown below.

       firstFamily lastFamily
number                       
1              man       girl
2              man      woman

I hope this helps.