python pandas custom agg function

Question

Dataframe:
  one two
a  1  x
b  1  y
c  2  y
d  2  z
e  3  z

grp = DataFrame.groupby(\'one\')
grp.agg(lambda x: ???) #or equivalent function

Desired o

Answer 1

There is a better way to concatenate strings, in pandas documentation.
So I prefer this way:

In [1]: df.groupby('one').agg(lambda x: x.str.cat(sep='|'))
Out[1]:
     two
one
1    x|y
2    y|z
3      z