[Numpy-discussion] sum of positive values in an array
Fri Sep 5 14:12:15 CDT 2008
thank you very much, deliciously satisfying
On Sep 5, 3:33 pm, Zachary Pincus <zachary.pin...@yale.edu> wrote:
> > Hi, probably a basic question, but I'm looking for a neat way to sum
> > all the positive values in an array of floats. I'm currently doing it
> > the hard way, but am hoping there is some cunning and elegant syntax I
> > can use instead
> Fancy indexing's my favorite cunning and elegant syntax:
> a = numpy.random.randn(100)
> a > 0 # gives a boolean array that's True where the elements of a are
> > 0.
> a[a > 0] # retrieve from a only the elements with True in the boolean
> a[a > 0].sum() # your desired result.
> Note that you can also fancy-index with a list/array of indices, as
> well as a boolean "mask" array:
> a[[1, 40, 55]] # pulls just the values at index 1, 40, and 55 out of a
> into a shape (3,) array.
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