Python: One-liner to perform an operation upon elements in a 2d array (list of lists)?

python arrays matrix 2d operation
aped picture aped · Jun 17, 2011 · Viewed 16.9k times · Source

I have a list of lists, each containing a different number of strings. I'd like to (efficiently) convert these all to ints, but am feeling kind of dense, since I can't get it to work out for the life of me. I've been trying: newVals = [int(x) for x in [row for rows in values]]

Where 'values' is the list of lists. It keeps saying that x is a list and can therefore not be the argument if int(). Obviously I'm doing something stupid here, what is it? Is there an accepted idiom for this sort of thing?

Answer

John La Rooy picture John La Rooy · Jun 17, 2011

This leaves the ints nested

[map(int, x) for x in values]

If you want them flattened, that's not hard either

for Python3 map() returns an iterator. You could use 

[list(map(int, x)) for x in values]

but you may prefer to use the nested LC's in that case

[[int(y) for y in x] for x in values]

Related questions

numpy matrix vector multiplication

When I multiply two numpy arrays of sizes (n x n)*(n x 1), I get a matrix of size (n x n). Following normal matrix multiplication rules, a (n x 1) vector is expected, but I simply cannot find any information …

Read More
Convert a 1D array to a 2D array in numpy

I want to convert a 1-dimensional array into a 2-dimensional array by specifying the number of columns in the 2D array. Something that would work like this: > import numpy as np > A = np.array([1,2,3,4,5,6]) > B = vec2matrix(…

Read More
Numpy matrix to array

I am using numpy. I have a matrix with 1 column and N rows and I want to get an array from with N elements. For example, if i have M = matrix([[1], [2], [3], [4]]), I want to get A = array([1,2,3,4]). To achieve it, …

Read More