[Numpy-discussion] How to Keep An Array Two Dimensional

Tom Bennett tom.bennett at mail.zyzhu.net
Sun Nov 25 21:24:46 EST 2012


I am trying to extract n columns from an 2D array and then operate on the
extracted columns. Below is the code:

A is an MxN 2D array.

u = A[:,:n] #extract the first n columns from A

B = np.dot(u, u.T) #take outer product.

This code works when n>1. However, when n=1, u becomes an 1D array instead
of an Mx1 2D array and the code breaks down.

I wonder if there is any way to keep u=A[:,:n] an Mxn array no matter what
value n takes. I do not want to use matrix because array is more convenient
in other places.

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