Index of a list item that occurs multiple times

Question

I have the following code

items = ['a', 'a', 'b', 'a', 'c', 'c', 'd']
for x in items:
    print(x, end='')
    print(items.index(x), end='')
## out puts: a0a0b2a0c4c4d6

I understand that python finds the first item in the list to index, but is it possible for me to get an output of a0a1b2a3c4c5d6 instead? It would be optimal for me to keep using the for loop because I will be editing the list. edit: I made a typo with the c indexes

*editing the list* (like add/remove) - while it is traversed - don't do it — RomanPerekhrest, Oct 21 '19 at 18:48
use `enumerate` to get the index & the value at the same time. Or zip your list with `range(len(lst))` — Jean-François Fabre, Oct 21 '19 at 18:48
@RomanPerekhrest you can change the list values all right. You cannot remove or add items, agreed — Jean-François Fabre, Oct 21 '19 at 18:49
adding the index doesn't add much information to your data. Consider using a tuple if you want that, instead of a string — Jean-François Fabre, Oct 21 '19 at 18:50
@Jean-FrançoisFabre - I'm assuming that too but very used to random logic not being shared :) — Sayse, Oct 21 '19 at 18:52
A possible duplicate of [How to find all occurrences of an element in a list?](https://stackoverflow.com/questions/6294179/how-to-find-all-occurrences-of-an-element-in-a-list) — Trenton McKinney, Oct 21 '19 at 18:54

score 0 · Answer 1 · edited Oct 21 '19 at 18:58

0

And in case you really feel like doing it in one line:

EDIT - using .format or format-strings makes this shorter / more legible, as noted in the comments

items = ['a', 'a', 'b', 'a', 'c', 'c', 'd']
print("".join("{}{}".format(e,i) for i,e in enumerate(items)))

For Python 3.7 you can do

items = ['a', 'a', 'b', 'a', 'c', 'c', 'd']
print("".join(f"{e}{i}" for i, e in enumerate(items)))

ORIGINAL

items = ['a', 'a', 'b', 'a', 'c', 'c', 'd']
print("".join((str(e) for item_with_index in enumerate(items) for e in item_with_index[::-1])))

Note that the reversal is needed (item_with_index[::-1]) because you want the items printed before the index but enumerate gives tuples with the index first.

edited Oct 21 '19 at 18:58

Jean-François Fabre

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answered Oct 21 '19 at 18:53

Nathan

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`"".join("{}{}".format(e,i) for i,e in enumerate(items))` is shorter – Jean-François Fabre Oct 21 '19 at 18:54
True, though the first `in` should be a `for`. – Nathan Oct 21 '19 at 18:56
true, fixed.... can also do `"".join("{1}{0}".format(*t) for t in enumerate(items))`. This could go on and on – Jean-François Fabre Oct 21 '19 at 18:58
Well your code is shorter but more readable? For most new programmers one liners like this are very confusing and not readable. – Mike - SMT Oct 21 '19 at 19:00
that's a question of getting used to it. – Jean-François Fabre Oct 21 '19 at 19:01
@Mike-SMT you could also argue that "See Spot Run" is very confusing and not readable to most people new to the English language :) – b_c Oct 21 '19 at 19:08
1

@b_c True. Thought I think if you are going to answer with a one liner it might help to explain each part as they are harder to grasp for most who don't use them than something like a for loop with if statements. Many of these simpler questions are asked by the new and inexperienced. – Mike - SMT Oct 21 '19 at 19:11

tw0shoes · Answer 2 · 2019-10-21T19:25:39.603

0

I think you're looking for a0a1b2a3c4c5d6 instead.

for i, x in enumerate(items):
    print("{}{}".format(x,i), end='')

edited Oct 21 '19 at 19:25

answered Oct 21 '19 at 18:55

tw0shoes

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rma · Accepted Answer · 2019-10-21T21:35:36.283

-1

Don't add or remove items from your list as you are traversing it. If you want the output specified, you can use enumerate to get the items and the indices of the list.

items = ['a', 'a', 'b', 'a', 'c', 'c', 'd']
for idx, x in enumerate(items):
    print("{}{}".format(x, idx), end='')
# outputs a0a1b2a3c4c5d6

edited Oct 21 '19 at 21:35

answered Oct 21 '19 at 18:51

rma

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Your first set of parenthesis are not needed and your are concatenation with `+` instead of `format()`. I would remove the parenthesis from `(idx, x)` to be more dry and note that `+` is deprecated over `format()`. – Mike - SMT Oct 21 '19 at 19:18
Almost there. You can remove `str()` as well as format handles the conversion. – Mike - SMT Oct 21 '19 at 19:31

Index of a list item that occurs multiple times

3 Answers3