Numpy transpose of 1D array not giving expected result

Question

I am trying a very basic example in Python scipy module for transpose() method but it's not giving expected result. I am using Ipython with pylab mode.

a = array([1,2,3] print a.shape >> (3,)  b = a.transpose() print b.shape >> (3,) 

If I print the contents of arrays "a" and "b", they are similar.

Expectation is: (which will be result in Matlab on transpose)

 [1,   2,   3] 

Answer 1

NumPy's transpose() effectively reverses the shape of an array. If the array is one-dimensional, this means it has no effect.

In NumPy, the arrays

array([1, 2, 3]) 

and

array([1,        2,        3]) 

are actually the same – they only differ in whitespace. What you probably want are the corresponding two-dimensional arrays, for which transpose() would work fine. Also consider using NumPy's matrix type:

In [1]: numpy.matrix([1, 2, 3]) Out[1]: matrix([[1, 2, 3]])  In [2]: numpy.matrix([1, 2, 3]).T Out[2]:  matrix([[1],         [2],         [3]]) 

Note that for most applications, the plain one-dimensional array would work fine as both a row or column vector, but when coming from Matlab, you might prefer using numpy.matrix.