plydata.helper_verbs.tally

class plydata.helper_verbs.tally(*args, **kwargs)

Tally observations by group

tally is a convenient wrapper for summarise that will either call n or sum(n) depending on whether you're tallying for the first time, or re-tallying.

Parameters

datadataframe, optional

Useful when not using the >> operator.

weightsstr or array-like, optional

Weight of each row in the group.

sortbool, optional

If True, sort the resulting data in descending order.

Examples

>>> import pandas as pd
>>> from plydata import tally, group_by, summarize
>>> df = pd.DataFrame({
...     'x': [1, 2, 3, 4, 5, 6],
...     'y': ['a', 'b', 'a', 'b', 'a', 'b'],
...     'w': [1, 2, 1, 2, 1, 2]})

Without groups it is one large group

>>> df >> tally()
   n
0  6

Sum of the weights

>>> df >> tally('w')
    n
0   9

With groups

>>> df >> group_by('y') >> tally()
   y  n
0  a  3
1  b  3

With groups and weights

>>> df >> group_by('y') >> tally('w')
   y  n
0  a  3
1  b  6

Applying the weights to a column

>>> df >> group_by('y') >> tally('x*w')
   y  n
0  a  9
1  b 24

You can do that with summarize

>>> df >> group_by('y') >> summarize(n='sum(x*w)')
   y  n
0  a  9
1  b 24