[SciPy-user] counting pairs of values
Thu Jul 16 09:48:55 CDT 2009
Check out the discussion from yesterday on the numpy list "Neighbour-
frequency matrix" for a generalization of this problem. You could also
use numpy.histogram2d for this.
On Jul 16, 2009, at 10:01 AM, Ernest Adrogué wrote:
> I've got a series of observations that consist of pairs of
> values (x, y) and I'm interested in counting the number of
> occurrences of arbitrary pairs of values.
> For example, if "a" is a 2-dimensional array such as
> array([[1, 2],
> [3, 4],
> [5, 5],
> [1, 2]])
> I want to find out how many (1, 2), or how many (3, 3) there
> Currently I'm doing this:
> numpy.logical_and(a[:,0] == 1, a[:,1] == 2).sum()
> which seems to work well enough, but I wonder if there's a
> more elegant/correct way of doing it.
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