[Numpy-discussion] Slicing/selection in multiple dimensions simultaneously
Mike Ressler
mike.ressler@alum.mit....
Tue Sep 11 17:11:53 CDT 2007
The following seems to be a wart: is it expected?
Set up a 10x10 array and some indexing arrays:
a=arange(100)
a.shape=(10,10)
q=array([0,2,4,6,8])
r=array([0,5])
Suppose I want to extract only the "even" numbered rows from a - then
print a[q,:]
<works - output deleted>
Every fifth column:
print a[:,r]
<works - output deleted>
Only the even rows of every fifth column:
print a[q,r]
---------------------------------------------------------------------------
<type 'exceptions.ValueError'> Traceback (most recent call last)
/.../.../.../<ipython console> in <module>()
<type 'exceptions.ValueError'>: shape mismatch: objects cannot be
broadcast to a single shape
But, this works:
print a[q,:][:,r]
[[ 0 5]
[20 25]
[40 45]
[60 65]
[80 85]]
So why does the a[q,r] form have problems? Thanks for your insights.
Mike
--
mike.ressler@alum.mit.edu
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