CODEWITHSUNDEEP
pythonloopsnested-lists
Tomasz Golinski
Tomasz Golinski

Reputation: 728

cleaning my list

Hello I have a loop which goes counts different records in my MySQL database and then saves the numbers to a list. Here is the list:
[1L, 2L, 2L, 5L, 4L, 1L, 1L, 1L, 3L, 1L, 1L, 2L, 2L, 3L, 3L, 1L, 2L, 4L, 2L, 1L, 3L, 1L, 2L, 4L, 1L, 2L, 1L, 1L, 3L, 1L, 3L, 1L, 5L, 2L, 1L, 1L, 5L, 1L, 1L, 1L, 4L, 2L, 1L, 3L, 2L, 1L, 2L, 2L, 2L, 3L, 1L, 1L, 3L, 2L, 2L, 1L, 3L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 3L, 3L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L]

now I go thru this list and I want to leave only single numbers (means 1L, 2L etc) I'm using this loop: 

for number in legend:
        print number # to check what number it does currently
        counter = legend.count(number)
        while counter > 1:
            legend.remove(number)
            counter -= 1

then I see that it checks 1,2,3,4,3,2,1 ...why is that? why this loop wont check number 5? at the end the list looks like this:
[5L, 5L, 5L, 4L, 3L, 2L, 1L]

that means it works but why it doesn't go for number 5?

thx in advance

Upvotes: 0

Views: 333

Answers (2)

berni
berni

Reputation: 1975

You might fall into problem such as:

list = [1,2,3,4]
for l in list:
    print "Elem ", l
    if l == 2:
        list.remove(1)

which gives output:

Elem  1
Elem  2
Elem  4

List is modified in loop and while removing some element that you already looped through you are skipping one element in list.

Upvotes: 0

Björn Pollex
Björn Pollex

Reputation: 76838

Just put it in a set.

>>> foo = [1,1,1,2,2,3,3,4,1,4,3,6,5,6]
>>> set(foo)
set([1, 2, 3, 4, 5, 6])

This will automatically filter out all duplicates. Maybe you can even skip the list, and put it in a set in the first place.

Upvotes: 7

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