[Numpy-discussion] conditional array indexing

Paul F. Dubois paul at pfdubois.com
Mon Jan 28 13:21:02 CST 2002


import Numeric, sys
a = Numeric.array([1,2,1,2,4,3,1,2,3,2,3,2])
b = Numeric.array([4,3,5,2,4,5,3,6,3,2,5,6])
c = Numeric.arange(len(b))

print c[Numeric.argmin(Numeric.where(a==1, b, sys.maxint))]


-----Original Message-----
From: numpy-discussion-admin at lists.sourceforge.net
[mailto:numpy-discussion-admin at lists.sourceforge.net] On Behalf Of
Michaell Taylor
Sent: Monday, January 28, 2002 12:59 PM
To: numpy-discussion at lists.sourceforge.net
Subject: [Numpy-discussion] conditional array indexing



Very new user to Numpy, so excuse the question.  It relates to a
fundamental 
issue which I have having trouble getting a grip on.

Specifically, say I have the following:

a = ([1,2,1,2,4,3,1,2,3,2,3,2])
b = ([4,3,5,2,4,5,3,6,3,2,5,6])
c = random variable of length=len(b)

I would like to get the value of C associated with the lowest value of b

within groupings of a.  That is, there are three incidents of "1" in the
a 
array.  The lowest value of b associated with the value 1 in the a index
is 
"3".  This occurs in index value 6 on the a and b arrays.  Now, I would
like 
to then know the value of c[6].  

Obviously the real problem is far more complex with len(a)==5000.  
Any ideas?  

Thanks in advance.

Michaell

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