Getting a "for" loop to remove characters from list if they are equal

Question

In my program, the user inputs a secret word that another person is to guess (hangman). The letters are then put into a list. I am trying to make a loop that checks if there are several equal letters in the list, and remove them if there is. This I have managed. The problem is that this loop also removes other characters that are not ment to be removed.

word = []

for i in range(int(len(secret_word)) - 1):
    if word[l] == word[q]:
        word.pop(l)
        q += 1
        if q > int(len(word)):
            break
    else:
        l +=1

Using the word "secret" and then printing the list, the output I get is

['s', 'c', 'e', 't']

It has removed the e, but unfortunately the r is also removed. Also, this loop doesn't remove a third equal letter. Using "secretive" the output is

['s', 'c', 'e', 'i', 'e']

Here, removing one of the e's, but also r, t and v

@vault Welcome to Stack Overflow. Don't forget to add the programming language as a tag for your post, so that you may receive directed answers. — fabio.avigo, Oct 05 '18 at 12:13
@vault of course you can, there's an [edit] button underneath it — UnholySheep, Oct 05 '18 at 12:14
And since this is now tagged as Python, what's wrong with just `set(word)` (or `list(set(word))` if you really need a list)? — UnholySheep, Oct 05 '18 at 12:16
@UnholySheep i'm not familiar with this statement, pass a link please? — vault, Oct 05 '18 at 12:18
Maybe have a look at [Removing duplicate characters from a string](https://stackoverflow.com/questions/9841303/removing-duplicate-characters-from-a-string) — Ian, Oct 05 '18 at 12:20
One piece of advise: if you want to remove items from whatever collection, always start at the end and move backwards to the first entry. — Dominique, Oct 05 '18 at 12:42

score 0 · Answer 1 · answered Oct 05 '18 at 12:21

0

word = 'secretblahblahset'
result = ''

for c in word:
  if not c in result:
    result += c 

print(result)

answered Oct 05 '18 at 12:21

Tohmaxxx

423
2
9

This doesn't answer the (implied) question as to why OP's code doesn't work – Ian Oct 05 '18 at 12:23
it doesn't work because he's iterating over an array while it's being modified – Tohmaxxx Oct 05 '18 at 12:26
3

Your answer should include that then. Btw, I didn't mark you down. – Ian Oct 05 '18 at 12:27

score 0 · Accepted Answer · answered Oct 05 '18 at 12:37

Your example code is missing a number of features such as the initialization of q and l. And I suspect you must have an outer loop that you're not showing us, otherwise the example doesn't make a lot of sense (in the example as given word is just an empty list).

If you want all the unique letters in a string you can do so easily with set():

unique_letters = set(secret_word)

However, that will not preserve order. I don't know for your case if you even need to preserve order. But if you wanted to there are many ways to do so, often still involving set() but not necessarily. Here's one way:

unique_letters = []
seen = set()
for let in secret_word:
    if let in seen:
        continue

    unique_letters.append(let)
    seen.add(let)

Another way, as a one-liner, might be something like:

unique_letters = sorted(set(secret_word), key=secret_word.index)

Those are just a few examples. There are many ways to do this. I'm sorry I can't say exactly what's wrong with you code. The example is missing too much context. But you're probably overcomplicating the problem.

Getting a "for" loop to remove characters from list if they are equal

2 Answers2