How does the python range command work with lists?

Question

Hey everyone i have this issue here, i really can't make out what the problem is. I know that range(2) gives 0 and 1 for possible i. len(R) = 2. And lists starts with 0.

R = [[1,1],[5,5]]
for i in range(len(R)):
    if R[i][0] == R[i][1]:     
        R.remove(R[i])

the error:

if R[i][0] == R[i][1]:

IndexError: list index out of range

Consider using [``filter``](https://docs.python.org/3/library/functions.html#filter) for deleting items from a collection based on a simple predicate on item, in your case f.e. ``filter(lambda r: r[0] != r[1], R)`` — randomir, Jun 18 '17 at 19:12

score 2 · Answer 1 · edited Jun 18 '17 at 19:26

2

R = [[1,1],[5,5]]
R = [x for x in R if x[0] != x[1]]

It should be != instead of == since he wants to get the numbers that are not identical.

edited Jun 18 '17 at 19:26

Lukas Herman

170
2
9

answered Jun 18 '17 at 19:17

Błotosmętek

12,717
19
29

Owen Hempel · Answer 2 · 2017-06-19T01:33:50.057

-3

In general, It's much easier to iterate over the items in the list:

Removal_items =[]
for I in R:
  #I is now a variable that represents the object in the list, or I = R[0]...R[n] where n = len(r) -1
  if I[0] == I[1]:
  Removal_items.append(I)

for I in Removal_items:
  R.remove(I)

edited Jun 19 '17 at 01:33

answered Jun 18 '17 at 18:57

Owen Hempel

434
2
8

Oh that is of course another possibility to look at it! Thanks! I will try that! – Omatikaya Jun 18 '17 at 18:58
Nope, this won't work. It'll skip items after each removal. – Moses Koledoye Jun 18 '17 at 18:59
2

See eg https://stackoverflow.com/questions/6260089/strange-result-when-removing-item-from-a-list for why this does not work. – stephan Jun 18 '17 at 19:03
Thanks guys i see now why this indeed does not work! – Omatikaya Jun 18 '17 at 19:21
Ok this won't run verbatim but the idea is there. I'll fix er up – Owen Hempel Jun 19 '17 at 01:31

How does the python range command work with lists?

2 Answers2