Creating a list of non-repetitive elements from repetitive-elemets list. Using list-comprehansion only

Question

How can I convert this "for-loop" below to "list-comprehension? I want to create a list of non-repetitive elements from repetitive-elemets list.

many_colors = ['red', 'red', 'blue', 'black', 'blue']

colors = []
for c in many_colors:
  if not c in colors:
    colors.append(c)
# colors = ['red', 'blue', 'black']

I tried this (below) but error occurs that colors are not defined.

colors = [c for c in many_colors if not c in colors]

You are creating `colors`, which also means you should not reference it before it actually is created. — Austin, Apr 16 '20 at 12:17

score 0 · Accepted Answer · answered Apr 16 '20 at 12:17

0

You can use set in python which represents an unordered collection of unique elements.

Use:

colors = list(set(many_colors))
print(colors)

This prints:

['red', 'black', 'blue']

answered Apr 16 '20 at 12:17

Shubham Sharma

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score -1 · Answer 2 · answered Apr 16 '20 at 12:16

-1

Use a set to make your life easier:

colors = [c for c in set(many_colors)]

answered Apr 16 '20 at 12:16

jfaccioni

6,606
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score -1 · Answer 3 · answered Apr 16 '20 at 12:19

colors only exists after the completion of the comprehension. A comprehension might not even be optimal. You can do

colors = list(set(colors))

And if you want to keep the order of occurrence:

from collections import OrderedDict

colors = list(OrderedDict.fromkeys(many_colors))

Creating a list of non-repetitive elements from repetitive-elemets list. Using list-comprehansion only

3 Answers3