[Numpy-discussion] sum of positive values in an array

SimonPalmer simon.palmer@gmail....
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.sum()
> 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  
> array.
> 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.
>
> Zach
> _______________________________________________
> Numpy-discussion mailing list
> Numpy-discuss...@scipy.orghttp://projects.scipy.org/mailman/listinfo/numpy-discussion


More information about the Numpy-discussion mailing list