Python 2d array iteration

Question

I have two lists, one with a parameter name and one with a pin name, and I am trying to combine the two lists into a 2d matrix but I cannot get the syntax right.

For example:

list1 = [parm1,parm2,parm3]
list2 = [end1,end2,end3]

and I want the matrix to be:

matrix1= [[parm1+ end1,parm1+end2, parm1+end3]
          [parm2+ end1,parm2+end2, parm2+end3]
          [parm3+ end1,parm3+end2, parm3+end3]

right now my code is

for i in range(len(parm_name)):
    for j in range(len(end_name)):
        pin_name[i][j] = parm_name[i] + end_name[j]

and it's not working.

What error are you getting? See: http://stackoverflow.com/q/6667201/3465172 — Bobbyrogers, Aug 13 '15 at 18:53

score 2 · Accepted Answer · answered Aug 13 '15 at 18:54

Instead of reassigning elements of a preinitialized list, simply create a new one:

list1 = [parm1,parm2,parm3]
list2 = [end1,end2,end3]
matrix1 = [[p+e for e in list2] for p in list1]

That last line can be expanded into the following equivalent code:

matrix1 = []
for p in list1:
    result = []
    for e in list2:
        result.append(p+e)
    matrix1.append(result)

score 1 · Answer 2 · answered Aug 13 '15 at 18:56

You can create matrix1 with the following:

matrix1 = [[p_name + e_name for e_name in list2] for p_name in list1]

You don't give much code so it's difficult to say why yours isn't working. I suspect that you don't initialize your matrix appropriately. But you don't need to initialize then assign, you can do it all in one step with list comprehension

Python 2d array iteration

2 Answers2