如何“减少”列表中的重复

Question

I am having trouble thinking of the most efficient way to reduce repetitions in a list.

a = ['x','x','x','y','y','y','z','z','z','x','x','x','z','z','z','z','z','z']

The desired output (if I reduce sets of 3) would be:

a_reduced = ['x','y','z','x','z','z']

I was thinking of looping through each element and do a '[i] and [i+1] and [i+2] condition' thing, but I am sure there is a super easy and efficient way to achieve this and that I am just missing something. Assist please, thanks!

Answer 1

If your repetitions are always in sets of 3 you could simply do:

a = ['x','x','x','y','y','y','z','z','z','x','x','x','z','z','z','z','z','z']
a_reduced = a[::3]
print a_reduced
>>>['x', 'y', 'z', 'x', 'z', 'z']

This will just grab every 3rd element from the list. Again, this is assuming your list is always in sets of 3. It will be skewed if they are not. Otherwise you if you just want to condense all of the unique repetitions as they go you can use itertools.groupby which will do just that:

from itertools import groupby
a = ['x','x','x','y','y','y','z','z','z','x','x','x','z','z','z','z','z','z']
a_reduced = [item[0] for item in groupby(a)]
print a_reduced
>>>['x', 'y', 'z', 'x', 'z']