Identify duplicate values in a list in Python

Question

Is it possible to get which values are duplicates in a list using python   I have a list of items       mylist    20  30  25  20    I know the best way of removing the duplicates is set mylist   but is it possible to know what values are being duplicated  As you can see  in this list the duplicates are the first and last values   0  3    Is it possible to get this result or something similar in python  I m trying to avoid making a ridiculously big if elif conditional statement

User · Answer

It looks like you want the indices of the duplicates  Here is some short code that will find those in O n  time  without using any packages  dups       dups setdefault v      append i  for i  v in enumerate mylist   dups    k  v for k  v in dups items   if len v   gt  1    dups now has keys for all the duplicate values   and a list of matching indices for each    The second line produces an unused list     It could be replaced with this  for i  v in enumerate mylist       dups setdefault v      append i

User · Answer

The following list comprehension will yield the duplicate values    x for x in mylist if mylist count x   gt   2

User · Answer

The following code will fetch you desired results with duplicate items and their index values     for i in set mylist       if mylist count i   gt  1           print i  mylist index i

User · Answer

You should sort the list   mylist sort     After this  iterate through it like this   doubles      for i  elem in enumerate mylist       if i    0          if elem    old              doubles append elem              old   None             continue     old   elem

User · Answer

You can use list compression and set to reduce the complexity   my list    3  5  2  1  4  4  1  opt    item for item in set my list  if my list count item   gt  1

User · Answer

m   len mylist  for index value in enumerate mylist           for i in xrange 1 m                   if index    i                       if  L i     L index                            print  Location  d and location  d has same list-entry    r     index i value    This has some redundancy that can be improved however

User · Answer

Here s a list comprehension that does what you want  As  Codemonkey says  the list starts at index 0  so the indices of the duplicates are 0 and 3    gt  gt  gt   i for i  x in enumerate mylist  if mylist count x   gt  1   0  3

User · Answer

def checkduplicate lists     a       for i in lists      if  i in a          pass        else          a append i   return i                        print checkduplicate  1 9 78 989 2 2 3 6 8

User · Answer

simplest way without any intermediate list using list index     z     a    b    a    c    b    a      z i  for i in range len z   if i    z index z i     gt  gt  gt   a    b    c     and you can also list the duplicates itself  may contain duplicates again as in the example     z i  for i in range len z   if not i    z index z i     gt  gt  gt   a    b    a     or their index    i for i in range len z   if not i    z index z i     gt  gt  gt  2  4  5    or the duplicates as a list of 2-tuples of their index  referenced to their first occurrence only   what is the answer to the original question        i z index z i    for i in range len z   if not i    z index z i     gt  gt  gt   2  0    4  1    5  0     or this together with the item itself     i z index z i   z i   for i in range len z   if not i    z index z i     gt  gt  gt   2  0   a     4  1   b     5  0   a      or any other combination of elements and indices

User · Answer

You can print duplicate and Unqiue using below logic using list   def dup x       duplicate          unique          for i in x          if i in unique              duplicate append i          else              unique append i      print  Duplicate values    duplicate      print  Unique Values    unique   list1    1  2  1  3  2  5  dup list1

User · Answer

These answers are O n   so a little more code than using mylist count   but much more efficient as mylist gets longer  If you just want to know the duplicates  use collections Counter  from collections import Counter mylist    20  30  25  20   k for k v in Counter mylist  items   if v gt 1    If you need to know the indices   from collections import defaultdict D   defaultdict list  for i item in enumerate mylist       D item  append i  D    k v for k v in D items   if len v  gt 1

User · Answer

I tried below code to find duplicate values from list  1  create a set of duplicate list  2  Iterated through set by looking in duplicate list   glist  1  2  3   one   5  6  1   one   x set glist  dup    for c in x      if glist count c  gt 1           dup append c  print dup    OUTPUT      1   one     Now get the all index for duplicate element  glist  1  2  3   one   5  6  1   one   x set glist  dup    for c in x      if glist count c  gt 1           indices    i for i  x in enumerate glist  if x    c          dup append  c indices   print dup    OUTPUT       1   0  6      one    3  7      Hope this helps someone

User · Answer

mylist    20  30  25  20   kl    i  mylist count i  for i in mylist if mylist count i   gt  1    print kl

User · Answer

That s the simplest way I can think for finding duplicates in a list   my list    3  5  2  1  4  4  1   my list sort   for i in range 0 len my list -1                  if my list i     my list i 1                      print str my list i       is a duplicate

[python] Identify duplicate values in a list in Python

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