Counting pairs of rows in pandas

I have this kind of Data Frame:

id  type
1   a
1   b
2   b
2   a
3   c
3   b

(Each ID has only 2 rows for sure)

I’d like to count the number of each pair, when a pair is the two types per ID.
I mean, to get that result for the previous table:

pair  count
(a, b)   2
(b, c)   1

Thanks!

>Solution :

You can use frozenset to have hashable, unordered objects to pass to value_counts:

df.groupby('id')['type'].agg(frozenset).value_counts()

output:

(a, b)    2
(b, c)    1
Name: type, dtype: int64

Note that the objects in the index are frozenset. I recommend to keep it this way (and to learn how to use them), but if you really need tuples:

out = df.groupby('id')['type'].agg(frozenset).value_counts()
out.index = out.index.map(tuple)