Python: Index an array using the colon operator in an arbitrary dimension

Question

I have a numpy nd array. A simplified version of my task is to take a vector from along each axis. To illustrate:

import numpy
x = numpy.array(range(24)).reshape         


        

Answer 1

You could compose an string with the code selecting the dimension you want and use eval to execute that code string.

An start is:

n = 2
sel = "0,"*(n-1) + ":"
eval('x[' + sel + ']')

To get exactly what you want, thinks are a little bit more complicated (but not so much):

ind = 2
n = 3
sel = "".join([ ("0" if i != ind else ":") + ("," if i < n-1 else "") for i in xrange(n)])
eval('x[' + sel + ']')

It is the same strategy that is used for Dynamic SQL.