List of all unique characters in a string

Question

I want to append characters to a string  but want to make sure all the letters in the final list are unique   Example   aaabcabccd     abcd   Now of course I have two solutions in my mind  One is using a list that will map the characters with their ASCII codes  So whenever I encounter a letter it will set the index to True  Afterwards I will scan the list and append all the ones that were set  It will have a time complexity of O n    Another solution would be using a dict and following the same procedure  After mapping every char  I will do the operation for each key in the dictionary  This will have a linear running time as well   Since I am a Python newbie  I was wondering which would be more space efficient  Which one could be implemented more efficiently   PS  Order is not important while creating the list

User · Answer

if the result does not need to be order-preserving  then you can simply use a set   gt  gt  gt     join set   aaabcabccd     acbd   gt  gt  gt

User · Answer

The simplest solution is probably   In  10      join set  aaabcabccd    Out 10    acbd    Note that this doesn t guarantee the order in which the letters appear in the output  even though the example might suggest otherwise   You refer to the output as a  list   If a list is what you really want  replace    join with list   In  1   list set  aaabcabccd    Out 1     a    c    b    d     As far as performance goes  worrying about it at this stage sounds like premature optimization

User · Answer

Store Unique characters in list  Method 1   uniue char   list set  aaabcabccd       a    b    c    d     Method 2  By Loop   Complex     uniue char      for c in  aaabcabccd       if not c in uniue char          uniue char append c  print uniue char     a    b    c    d

User · Answer

I have an idea  Why not use the ascii lowercase constant   For example  running the following code     string module  contains constant ascii lowercase which is all the lowercase   letters of the English alphabet import string   Example value of s  a string s    aaabcabccd    Result variable to store the resulting string result        Goes through each letter in the alphabet and checks how many times it appears    If a letter appears at least oce  then it is added to the result variable for letter in string ascii letters      if s count letter   gt   1          result  letter    Optional three lines to convert result variable to a list for sorting   and then back to a string result   list result  result sort   result      join result   print result    Will print  abcd   There you go  all duplicates removed and optionally sorted

User · Answer

Use an OrderedDict  This will ensure that the order is preserved   gt  gt  gt     join OrderedDict fromkeys   aaabcabccd   keys     abcd    PS  I just timed both the OrderedDict and Set solution  and the later is faster  If order does not matter  set should be the natural solution  if Order Matter s this is how you should do    gt  gt  gt  from timeit import Timer  gt  gt  gt  t1   Timer stmt stmt1  setup  from   main   import data  OrderedDict    gt  gt  gt  t2   Timer stmt stmt2  setup  from   main   import data    gt  gt  gt  t1 timeit number 1000  1 2893918431815337  gt  gt  gt  t2 timeit number 1000  0 0632140599081196

User · Answer

For completeness sake  here s another recipe that sorts the letters as a byproduct of the way it works    gt  gt  gt  from itertools import groupby  gt  gt  gt     join k for k  g in groupby sorted  aaabcabccd      abcd

User · Answer

char seen      for char in string      if char not in char seen          char seen append char  print    join char seen     This will preserve the order in which alphabets are coming    output will be  abcd

[python] List of all unique characters in a string?

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