I have a list of numbers that represent the flattened output of a matrix or array produced by another program, I know the dimensions of the original array and want to read the numbers back into either a list of lists or a NumPy matrix. There could be more than 2 dimensions in the original array.
e.g.
data = [0, 2, 7, 6, 3, 1, 4, 5]
shape = (2,4)
print some_func(data, shape)
Would produce:
[[0,2,7,6], [3,1,4,5]]
Cheers in advance
Use numpy.reshape:
>>> import numpy as np
>>> data = np.array( [0, 2, 7, 6, 3, 1, 4, 5] )
>>> shape = ( 2, 4 )
>>> data.reshape( shape )
array([[0, 2, 7, 6],
[3, 1, 4, 5]])
You can also assign directly to the shape attribute of data if you want to avoid copying it in memory:
>>> data.shape = shape
If you dont want to use numpy, there is a simple oneliner for the 2d case:
group = lambda flat, size: [flat[i:i+size] for i in range(0,len(flat), size)]
And can be generalized for multidimensions by adding recursion:
import operator
def shape(flat, dims):
subdims = dims[1:]
subsize = reduce(operator.mul, subdims, 1)
if dims[0]*subsize!=len(flat):
raise ValueError("Size does not match or invalid")
if not subdims:
return flat
return [shape(flat[i:i+subsize], subdims) for i in range(0,len(flat), subsize)]
For those one liners out there:
>>> data = [0, 2, 7, 6, 3, 1, 4, 5]
>>> col = 4 # just grab the number of columns here
>>> [data[i:i+col] for i in range(0, len(data), col)]
[[0, 2, 7, 6],[3, 1, 4, 5]]
>>> # for pretty print, use either np.array or np.asmatrix
>>> np.array([data[i:i+col] for i in range(0, len(data), col)])
array([[0, 2, 7, 6],
[3, 1, 4, 5]])
Without Numpy we can do as below as well..
l1 = [1,2,3,4,5,6,7,8,9]
def convintomatrix(x):
sqrt = int(len(x) ** 0.5)
matrix = []
while x != []:
matrix.append(x[:sqrt])
x = x[sqrt:]
return matrix
print (convintomatrix(l1))
