[Numpy-discussion] how to tally the values seen
Gökhan Sever
gokhansever@gmail....
Wed Apr 14 01:27:02 CDT 2010
On Wed, Apr 14, 2010 at 1:10 AM, Peter Shinners <pete@shinners.org> wrote:
> I have an array that represents the number of times a value has been
> given. I'm trying to find a direct numpy way to add into these sums
> without requiring a Python loop.
>
> For example, say there are 10 possible values. I start with an array of
> zeros.
>
> >>> counts = numpy.zeros(10, numpy.int)
>
> Now I get an array with several values in them, I want to add into
> counts. All I can think of is a for loop that will give my the results I
> want.
>
>
> >>> values = numpy.array((2, 8, 1))
> >>> for v in values:
> ... counts[v] += 1
> >>> print counts
> [0 1 1 0 0 0 0 0 1 0]
>
This is easy:
I[3]: a
O[3]: array([ 0., 1., 1., 0., 0., 0., 0., 0., 1., 0.])
I[4]: a = np.zeros(10)
I[5]: b = np.array((2,8,1))
I[6]: a[b] = 1
I[7]: a
O[7]: array([ 0., 1., 1., 0., 0., 0., 0., 0., 1., 0.])
Let me think about the other case :)
> I also need to handle the case where a value is listed more than once.
> So if values is (2, 8, 1, 2) then count[2] would equal 2.
>
> What is the most efficient way to do this?
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--
Gökhan
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