Python: Concatenate (or clone) a numpy array N times

Question

I want to create an MxN numpy array by cloning a Mx1 ndarray N times. Is there an efficient pythonic way to do that instead of looping?

Btw the following way doesn't work for me (X is my Mx1 array) :

   numpy.concatenate((X, numpy.tile(X,N))) 

since it created a [M*N,1] array instead of [M,N]

Answer 1

You are close, you want to use np.tile, but like this:

a = np.array([0,1,2]) np.tile(a,(3,1)) 

Result:

array([[0, 1, 2],    [0, 1, 2],    [0, 1, 2]]) 

If you call np.tile(a,3) you will get concatenate behavior like you were seeing

array([0, 1, 2, 0, 1, 2, 0, 1, 2]) 

http://docs.scipy.org/doc/numpy/reference/generated/numpy.tile.html

Answer 2

You could use vstack:

numpy.vstack([X]*N) 

e.g.

>>> import numpy as np >>> X = np.array([1,2,3,4]) >>> N = 7 >>> np.vstack([X]*N) array([[1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4],        [1, 2, 3, 4]])