How to sort a list of strings numerically

Question

I know that this sounds trivial but I did not realize that the sort   function of Python was weird  I have a list of  numbers  that are actually in string form  so I first convert them to ints  then attempt a sort   list1   1   10   3   22   23   4   2   200   for item in list1      item int item   list1 sort   print list1   Gives me     1    10    2    200    22    23    3    4     What I want is     1   2   3   4   10   22   23   200     I ve looked around for some of the algorithms associated with sorting numeric sets  but the ones I found all involve sorting alphanumeric sets    I know this is probably a no brainer problem but google and my textbook don t offer anything more or less useful than the  sort   function

User · Answer

If you want to use strings of the numbers better take another list as shown in my code it will work fine   list1   1   10   3   22   23   4   2   200    k        for item in list1          k append int item    k sort   print k     1  2  3  4  10  22  23  200

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In case you want to use sorted   function  sorted list1  key int   It returns a new sorted list

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You can also use    import re  def sort human l       convert   lambda text  float text  if text isdigit   else text     alphanum   lambda key   convert c  for c in re split    -    0-9      0-9      key       l sort key alphanum      return l   This is very similar to other stuff that you can find on the internet but also works for alphanumericals like  abc0 1  abc0 2

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Simple way to sort a numerical list  numlists     5   50   7   51   87   97   53   results   list map int  numlists   results sort reverse False  print results

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Python s sort isn t weird  It s just that this code   for item in list1     item int item    isn t doing what you think it is - item is not replaced back into the list  it is simply thrown away   Anyway  the correct solution is to use key int as others have shown you

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The most recent solution is right  You are reading solutions as a string  in which case the order is 1  then 100  then 104 followed by 2 then 21  then 2001001010  3 and so forth   You have to CAST your input as an int instead   sorted strings    stringList    1  10  2  21  3   sorted ints    intList    1  2  3  10  21   To cast  just put the stringList inside int   blahblah     Again    stringList    1  10  2  21  3   newList   int  stringList   print newList    gt  returns  1  2  3  10  21

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Seamus Campbell s answer doesnot work on python2 x  list1   sorted list1  key lambda e  int e   using lambda function works well

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real problem is that sort sorts things alphanumerically  So if you have a list   1    2    10    19   and run sort you get   1    10    19    2    ie 10 comes before 2 because it looks at the first character and sorts starting from that  It seems most methods in python return things in that order  For example if you have a directory named abc with the files labelled as 1 jpg  2 jpg etc say up to 15 jpg and you do file list os listdir abc  the file list is not ordered as you expect but rather as file list   1 jpg    11 jpg --- 15 jpg    2 jpg   If the order in which files are processed is important  presumably that s why you named them numerically  the order is not what you think it will be  You can avoid this by using  zeros  padding  For example if you have a list alist   01    03    05    10    02   04    06  and you run sort on it you get the order you wanted  alist   01    02  etc  because the first character is 0 which comes before 1  The amount of zeros padding you need is determined by the largest value in the list For example if the largest is say between 100 and 1000 you need to pad single digits as 001  002 ---010 011--100  101 etc

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I approached the same problem yesterday and found a module called  natsort  1   which solves your problem  Use  from natsort import natsorted   pip install natsort    Example list of strings a     1    10    2    3    11     In   sorted a   Out    1    10    11    2    3     In   natsorted a   Out    1    2    3    10    11      Your array may contain strings  In   natsorted   string11    string3    string1    string10    string100     Out    string1    string3    string10    string11    string100    It also works for dictionaries as an equivalent of sorted   1   https   pypi org project natsort

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Try this  it   ll sort the list in-place in descending order  there   s no need to specify a key in this case    Process  listB    24  13  -15  -36  8  22  48  25  46  -9  listC   sorted listB  reverse True    listB remains untouched print listC   output     48  46  25  24  22  13  8  -9  -15  -36

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You haven t actually converted your strings to ints   Or rather  you did  but then you didn t do anything with the results   What you want is   list1     1   10   3   22   23   4   2   200   list1    int x  for x in list1  list1 sort     If for some reason you need to keep strings instead of ints  usually a bad idea  but maybe you need to preserve leading zeros or something   you can use a key function  sort takes a named parameter  key  which is a function that is called on each element before it is compared  The key function s return values are compared instead of comparing the list elements directly   list1     1   10   3   22   23   4   2   200     call int x  on each element before comparing it list1 sort key int

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may be not the best python  but for string lists like   1   1 0   2 0   2    1 1    1 10    1 11    1 2   7   3   5  with the expected target   1    1 0    1 1    1 2    1 10    1 11    2    2 0    3    5    7   helped me    unsortedList     1   1 0   2 0   2    1 1    1 10    1 11    1 2   7   3   5   sortedList      sortDict      sortVal       set zero correct  integer   examp  1 000 will be 1 and breaks the order zero    quot 000 quot  for i in sorted unsortedList     x   i split  quot   quot     if x 0  in sortDict      if len x   gt  1          sortVal append x 1       else          sortVal append zero      sortDict x 0     sorted sortVal  key   int    else      sortVal          if len x   gt  1          sortVal append x 1       else          sortVal append zero      sortDict x 0     sortVal for key in sortDict    for val in sortDict key       if val    zero         sortedList append str key       else         sortedList append str key     quot   quot    str val   print sortedList

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scores     91   89   87   86   85   scores sort   print  scores    This worked for me using python version 3  though it didn t in version 2

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You could pass a function to the key parameter to the  sort method  With this  the system will sort by key x  instead of x   list1 sort key int      BTW  to convert the list to integers permanently  use the map function  list1   list map int  list1       you don t need to call list   in Python 2 x   or list comprehension  list1    int x  for x in list1

[python] How to sort a list of strings numerically?

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