In order to "concatenate" a few rows to 1 list with groupby in Pandas, I can do this:
df = pd.DataFrame({'A': [1,1,2,2,2,2,3],'B':['a','b','c','d','e','f','g']})
df = df.groupby('A')['B'].apply(list)
I will get:
A
-------------------
1 [a, b]
2 [c, d, e, f]
3 [g]
I want to do the same with agg:
f = {"B":[list]}
df = df.groupby('A').agg(f)
that gives errors, any idea?
Thanks,
You can use tolist - output is Series:
df = df.groupby('A')['B'].agg(lambda x: x.tolist())
print (df)
A
1 [a, b]
2 [c, d, e, f]
3 [g]
dtype: object
Or with define column B in dict - output is DataFrame:
df = df.groupby('A').agg({'B': lambda x: x.tolist()})
print (df)
B
A
1 [a, b]
2 [c, d, e, f]
3 [g]
Also works:
df = df.groupby('A')['B'].agg(lambda x: list(x))
print (df)
A
1 [a, b]
2 [c, d, e, f]
3 [g]
dtype: object
df = df.groupby('A').agg({'B': lambda x: list(x)})
print (df)
B
A
1 [a, b]
2 [c, d, e, f]
3 [g]
