[Numpy-discussion] ndarray.count() ?
Martin Spacek
scipy at mspacek.mm.st
Thu Sep 7 16:17:58 EDT 2006
What's the most straightforward way to count, say, the number of 1s or
Trues in the array? Or the number of any integer?
I was surprised to discover recently that there isn't a count() method
as there is for Python lists. Sorry if this has been discussed already,
but I'm wondering if there's a reason for its absence.
I came across a thread in March:
http://aspn.activestate.com/ASPN/Mail/Message/numpy-discussion/3066460
that talked a bit about this in terms of speed, but what about just the
convenience of having a count() method?
Looks like masked arrays have a count method, don't know much about them
though.
Also, I understand the inaccuracies when converting between binary and
decimal floating point representations, and therefore making counting of
a specific float value in an array somewhat undefined, yet it seems to
work in Python lists:
>>> 1.1
1.1000000000000001
>>> a=[1.1, 1.1, 1.2]
>>> a
[1.1000000000000001, 1.1000000000000001, 1.2]
>>> a.count(1.1)
2
>>> a.count(1.1000000000000001)
2
>>> a.count(1.2)
1
Comments?
Martin
More information about the NumPy-Discussion
mailing list