Extract part of 2D-List/Matrix/List of lists in Python

Question

I want to extract a part of a two-dimensional list (=list of lists) in Python. I use Mathematica a lot, and there it is very convenient to write

matrix[[2;;4,10;;13]]

which would extract the part of the matrix which is between the 2nd and 4th row as well as the 10th and 13th column.

In Python, I just used

[x[firstcolumn:lastcolumn+1] for x in matrix[firstrow:lastrow+1]]

Is there also a more elegant or efficient way to do this?

weronika · Accepted Answer · 2012-06-10 17:51:57Z

21

What you want is numpy arrays and the slice operator :.

>>> import numpy

>>> a = numpy.array([[1,2,3],[2,2,2],[5,5,5]])
>>> a
array([[1, 2, 3],
       [2, 2, 2],
       [5, 5, 5]])

>>> a[0:2,0:2]
array([[1, 2],
       [2, 2]])

answered Jun 10, 2012 at 17:51

weronika

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1 Comment

weronika Over a year ago

@user1447622 - you're welcome! If the answer works, you should accept it by clicking on the checkmark (unless you're waiting to see if you get other answers, which is perfectly fine - I just thought I'd point it out in case you didn't know how it works, since you're a new user)

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