Sampling From Each Group

[jeff-hernandez]

Closes #124 by adding the parameter per_instance, which determines whether or not the sampling should be applied to each group. Working through the code, it made sense to make this parameter boolean. This added more functionality by allowing users to sample a fraction of the labels from each group.

Example

>>> lt

   entity labels
0       0      a
1       0      a
2       0      b
3       0      b
4       1      a
5       1      a
6       1      b
7       1      b

>>> frac = {'a': 1, 'b': .5}
>>> lt.sample(frac=frac, per_instance=True)

   entity labels
0       0      a
1       0      a
2       0      b
4       1      a
5       1      a
7       1      b

[codecov]

Codecov Report

Merging #138 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #138   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        26           
  Lines         1064      1085   +21     
=========================================
+ Hits          1064      1085   +21     

Impacted Files	Coverage Δ
composeml/label_times/object.py	100.00% <100.00%> (ø)
...mposeml/tests/test_label_transforms/test_sample.py	100.00% <100.00%> (ø)

[frances-h]

👍 lgtm

[jeff-hernandez]

This PR was repurposed to apply the changes from #144.