Raise exception in Ideal_labeler when the given feature is not found

[yangarbiter]

https://github.com/ntucllab/libact/blob/interface-documentation/libact/labelers/ideal_labeler.py#L30

[lsc36]

Referring to master:
https://github.com/ntucllab/libact/blob/master/libact/labelers/ideal_labeler.py#L30

[lsc36]

Current IdealLabeler seems to return a list of labels instead of the label. This should also be fixed.

self.y[np.where([...])[0]]

should be

self.y[np.where([...])[0]][0]

or

self.y[np.where([...])[0][0]]

then catch IndexError and reraise ValueError to indicate feature not found.

[lsc36]

Opened issue #32. Please solve it first.

[lsc36]

#32 closed. Let's move discussion under #33.