Convert 1D array into numpy matrix

Question

I have a simple, one dimensional Python array with random numbers. What I want to do is convert it into a numpy Matrix of a specific shape. My current attempt looks like this:

randomWeights = []
for i in range(80):
    randomWeights.append(random.uniform(-1, 1))
W = np.mat(randomWeights)
W.reshape(8,10)

Unfortunately it always creates a matrix of the form:

[[random1, random2, random3, ...]]

So only the first element of one dimension gets used and the reshape command has no effect. Is there a way to convert the 1D array to a matrix so that the first x items will be row 1 of the matrix, the next x items will be row 2 and so on?

Basically this would be the intended shape:

[[1, 2, 3, 4, 5, 6, 7, 8],
 [9, 10, 11, ... ,    16],
 [...,               800]]

I suppose I can always build a new matrix in the desired form manually by parsing through the input array. But I'd like to know if there is a simpler, more eleganz solution with built-in functions I'm not seeing. If I have to build those matrices manually I'll have a ton of extra work in other areas of the code since all my source data comes in simple 1D arrays but will be computed as matrices.

Why is there the number 800 in the last element, and not 80? — MasterControlProgram
– MasterControlProgram, Commented Sep 17, 2019 at 17:28

Junuxx · Accepted Answer · 2013-04-26 11:44:16Z

28

reshape() doesn't reshape in place, you need to assign the result:

>>> W = W.reshape(8,10)
>>> W.shape
(8,10)

answered Apr 26, 2013 at 11:44

Junuxx

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MasterControlProgram Over a year ago

It should be reshape(10,8) for the intended 10 x 8 matrix, btw

Han Qiu · Accepted Answer · 2016-04-26 10:05:42Z

2

You can use W.resize(), ndarray.resize()

answered Apr 26, 2016 at 10:05

Han Qiu

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