[Numpy-discussion] Count the occurrence of a certain integer in a list of integers

Mark.Miller mpmusu@cc.usu....
Wed Aug 8 11:26:24 CDT 2007


A late entry, but here's something that gets you an array of counts for 
each unique integer:

 >>> data = numpy.array([9, 6, 9, 6, 7, 9, 9, 10, 7, 9, 9, 6, 7, 9, 8, 
8, 11, 9, 6, 7, 10, 9, 7, 9, 7, 8, 9, 8, 7, 9])
 >>> unique=numpy.unique(data)
 >>> unique
array([ 6,  7,  8,  9, 10, 11])
 >>> histo=numpy.histogram(data,unique)
 >>> histo
(array([ 4,  7,  4, 12,  2,  1]), array([ 6,  7,  8,  9, 10, 11]))
 >>>

So histo[0] includes the counts of each integer in data.

-Mark


2007/8/7, Nils Wagner <nwagner@iam.uni-stuttgart.de>:
 >
 > Hi all,
 >
 > I have a list of integer numbers. The entries can vary between 0 and 19.
 > How can I count the occurrence of any number. Consider
 >
 > >>> data
 > [9, 6, 9, 6, 7, 9, 9, 10, 7, 9, 9, 6, 7, 9, 8, 8, 11, 9, 6, 7, 10, 9, 7,
 > 9, 7, 8, 9, 8, 7, 9]
 >
 >
 > Is there a better way than using, e.g.
 >
 > >>> shape(where(array(data)==10))[1]
 > 2
 >
 >
 > to compute the occurrence of 10 in the list which is 2 in this case ?
 >
 > Nils


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