Issue
I have a matrix A
, and a (list of tuples) corresponding to coordinates C
. How do I get A[C]
?
For example:
>>> A
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14],
[15, 16, 17, 18, 19],
[20, 21, 22, 23, 24]])
>>> C
[(0,0), (1,2), (4,-1)]
The function I want, but don't know the name of, works like this:
>>> func(A,C)
[0, 7, 24]
Does such a function (or some funky NumPy indexing syntax) exist, or is a for
loop the only way to get this result?
Solution
You have a list of X,Y
pairs. That can't be fed directly to an arrays indexer - it needs to be changed a bit.
Instead of [(X,Y), (X,Y), (X,Y)]
, you need [(X,X,X), (Y,Y,Y)]
:
>>> x = [x for x,y in C]
>>> y = [y for x,y in C]
>>> A[x, y]
array([ 0, 7, 24])
Or even simpler:
>>> A[tuple(zip(*C))]
array([ 0, 7, 24])
Answered By - richardec
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