Remove a column from a nested list in Python

Question

I need help figuring how to work around removing a 'column' from a nested list to modify it.

Say I have

L = [[1,2,3,4],
     [5,6,7,8],
     [9,1,2,3]]

and I want to remove the second column (so values 2,6,1) to get:

L = [[1,3,4],
     [5,7,8],
     [9,2,3]]

I'm stuck with how to modify the list with just taking out a column. I've done something sort of like this before? Except we were printing it instead, and of course it wouldn't work in this case because I believe the break conflicts with the rest of the values I want in the list.

def L_break(L):

i = 0
while i < len(L):
    k = 0
    while k < len(L[i]):
        print( L[i][k] , end = " ")
        if k == 1:
            break
        k = k + 1
    print()
    i = i + 1

So, how would you go about modifying this nested list? Is my mind in the right place comparing it to the code I have posted or does this require something different?

Answer 1

You can simply delete the appropriate element from each row using del:

L = [[1,2,3,4],      [5,6,7,8],      [9,1,2,3]]  for row in L:     del row[1]  # 0 for column 1, 1 for column 2, etc.  print L # outputs [[1, 3, 4], [5, 7, 8], [9, 2, 3]] 

Answer 2

If you want to extract that column for later use, while removing it from the original list, use a list comprehension with pop:

>>> L = [[1,2,3,4],
...       [5,6,7,8],
...       [9,1,2,3]]
>>> 
>>> [r.pop(1) for r in L]
[2, 6, 1]
>>> L
[[1, 3, 4], [5, 7, 8], [9, 2, 3]]

Otherwise, just loop over the list and delete the fields you no longer want, as in arshajii's answer