Converting List of Numpy Arrays to Numpy Matrix

Question

I have a list of lists, lists which I would like to convert to a numpy matrix (which I would usually do by matrixA = np.matrix(lists). The len of each list in lists is 7000, and the len(lists) is 10000.

So when I perform matrixA = np.matrix(lists), I would expect that np.shape(matrixA) to return (10000, 7000). However it instead returns (10000, 1) where each element is an ndarray.

This has never happened to me before, but I absolutely need this to be in the form of (10000, 7000). Might anyone have a suggestion about how to get this in the proper format?

• Akavall: Can you reproduce this with a small example?
• Akavall: And are your sublists of the same length?

Answer 1

I tried to recreate, but I can't:

>>> import numpy as np
>>> arrs = np.random.randn(10000, 7000)
>>> arrs
array([[ 1.07575627, 0.16139542, 1.92732122, ..., -0.26905029,
 0.73061849, -0.61021016],
 [-0.61298112, 0.58251565, -1.0204561 , ..., 1.73095028,
 0.25763494, 0.03769834],
 [ 1.08827523, 1.67841947, -0.08118218, ..., -0.4315941 ,
 1.41509082, 0.59479981],
 ..., 
 [ 0.7457839 , 0.20886401, 1.07463208, ..., 0.79508743,
 0.15184803, -0.34028477],
 [-0.25272939, 0.17744917, -1.45035157, ..., -0.54263528,
 0.04489259, -0.41222399],
 [ 1.58635482, 2.2273889 , 1.1803809 , ..., 0.8501827 ,
 -0.43804703, 0.78975036]])
>>> lists = [list(arr) for arr in arrs]
>>> len(lists)
10000
>>> all(len(lis) == 7000 for lis in lists)
True
>>> mat = np.matrix(lists)

and mat is now:

>>> mat
matrix([[ 1.07575627, 0.16139542, 1.92732122, ..., -0.26905029,
 0.73061849, -0.61021016],
 [-0.61298112, 0.58251565, -1.0204561 , ..., 1.73095028,
 0.25763494, 0.03769834],
 [ 1.08827523, 1.67841947, -0.08118218, ..., -0.4315941 ,
 1.41509082, 0.59479981],
 ..., 
 [ 0.7457839 , 0.20886401, 1.07463208, ..., 0.79508743,
 0.15184803, -0.34028477],
 [-0.25272939, 0.17744917, -1.45035157, ..., -0.54263528,
 0.04489259, -0.41222399],
 [ 1.58635482, 2.2273889 , 1.1803809 , ..., 0.8501827 ,
 -0.43804703, 0.78975036]])
>>> mat.shape
(10000, 7000)