IndexError when evaluating ndarray with indexes in another ndarray

Question

I'm trying to get values from an ndarray with indices in another ndarray but I keep getting this error

IndexError too many indices for array.

The array that I'm trying to get the values from, scores , has scores.shape = (10,10000) and the array pointing out the indices, indices , has indices.shape = (10000,2)

I'm trying to get the values this way:

values = scores[tuple(indices)]

but this is where I get the error.

What I'm trying to do this way is to access several individual values of scores, e.g. scores[0,6], scores[1,9] in another array so I get something like

[scores[0,6],scores[1,9],...]

all in one go and avoiding loops. Those [[0,6] , [1,9], ...] are stored in the indices array. I mention the previous in case that could lead to a work around.

cge · Accepted Answer · 2016-02-18 19:39:07Z

2

Try the following: scores[indices[:,0],indices[:,1]]. Or alternatively, scores[tuple(indices.T)].

When you do scores[tuple(indices)], tuple(indices) is creating a tuple of 2-element arrays. Numpy interprets this as you trying to get 2 elements of a 10,000 dimensional array! For the sort of indexing you need, Numpy expects arrays of values for each dimension. In other words, rather than ( [x1,y1], [x2,y2] ), it wants ( [x1,x2], [y1, y2] ).

edited Feb 18, 2016 at 19:39

answered Feb 18, 2016 at 19:23

cge

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1 Comment

Diego Aguado Over a year ago

The last line you wrote down illuminated me so much! Thanks @cge ;)

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