[Numpy-discussion] Histograms via indirect index arrays
Mads Ipsen
mpi at osc.kiku.dk
Tue Mar 14 13:24:11 CST 2006
Hey,
First of all, thanks for the new release.
Here's another question regarding something I cannot quite understand:
Suppose you want to update bins for a histogram, you might think you
could do something like:
g = zeros(4,Int)
x = array([0.2, 0.2])
idx = floor(x/0.1).astype(int)
g[idx] += 1
Here idx becomes
array([2, 2])
In this case, I would naively expect g to end up like
array([0, 0, 2, 0]) (1)
but instead you get
array([0, 0, 1, 0]) (2)
Is this intended? Just being plain novice-like naive, I would expect
the slice operation g[idx] += 1 to do something like
for i in range(len(I)):
g[ idx[i] ] += 1
resulting in (1) and not (2).
// Mads
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