How to sort and remove duplicates from Python list?

jmglov_58994 0
Viewed 152883

Given a list of strings, I want to sort it alphabetically and remove duplicates. I know I can do this:

from sets import Set
[...]
myHash = Set(myList)

but I don't know how to retrieve the list members from the hash in alphabetical order.

I'm not married to the hash, so any way to accomplish this will work. Also, performance is not an issue, so I'd prefer a solution that is expressed in code clearly to a fast but more opaque one.

unique list sorting python
6 Answers

A list can be sorted and deduplicated using built-in functions:

myList = sorted(set(myList))
  • set is a built-in function for Python >= 2.3
  • sorted is a built-in function for Python >= 2.4
Rod_Daunoravicius_209890

If your input is already sorted, then there may be a simpler way to do it:

from operator import itemgetter
from itertools import groupby
unique_list = list(map(itemgetter(0), groupby(yourList)))
sykora_538500

If it's clarity you're after, rather than speed, I think this is very clear:

def sortAndUniq(input):
  output = []
  for x in input:
    if x not in output:
      output.append(x)
  output.sort()
  return output

It's O(n^2) though, with the repeated use of not in for each element of the input list.

unwind_281690

> but I don't know how to retrieve the list members from the hash in alphabetical order.

Not really your main question, but for future reference Rod's answer using sorted can be used for traversing a dict's keys in sorted order:

for key in sorted(my_dict.keys()):
   print key, my_dict[key]
   ...

and also because tuple's are ordered by the first member of the tuple, you can do the same with items:

for key, val in sorted(my_dict.items()):
    print key, val
    ...
user_82470
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