[Numpy-discussion] Indexing issue with ndarrays

Joseph Fox-Rabinovitz jfoxrabinovitz at gmail.com
Thu Aug 25 10:36:50 EDT 2016

This issue recently came up on Stack Overflow:
The poster attempted to index an ndarray with a pandas boolean Series
object (all False), but the result was as if he had indexed with an array
of integer zeros.

Can someone explain this behavior? I can see two obvious possibilities:

   1. ndarray checks if the input to __getitem__ is of exactly the right
   type, not using instanceof.
   2. pandas actually uses a wider datatype than boolean internally, so
   indexing with the series is in fact indexing with an integer array.

In my attempt to reproduce the poster's results, I got the following

FutureWarning: in the future, boolean array-likes will be handled as a
boolean array index

This indicates that the issue is probably #1 and that a fix is already on
the way. Please correct me if I am wrong. Also, where does the code for
ndarray.__getitem__ live?


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