[Numpy-discussion] using the functions nonzero and where

Christopher Barker Chris.Barker@noaa....
Tue Apr 24 12:34:52 CDT 2007


Bill Baxter wrote:
>> In [35]: x = [ 0, 0, 0, 99, 0, 1, 5]
>> In [37]: i=nonzero(x)
>> In [38]: i
>> Out[38]: (array([3, 5, 6]),)

> Just do i[0].  It's an array, not a string.  Try typing "type(i[0])"
> and see what it tells you.

Which still begs the question: why does nonzero() return a tuple with an 
array in it, rather than just the array?

Is it so you can so this?

 >>> a = numpy.array(((3,0,4),(5,21,0)))

 >>> numpy.nonzero(a)
(array([0, 0, 1, 1]), array([0, 2, 0, 1]))

 >>> a[numpy.nonzero(a)]
array([ 3,  4,  5, 21])

-Chris


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