How to remove multiple indexes from a list at the same time

Question

Say I have this list here   list    a  b  c  d  e  f  g    How would I delete say indexes 2  3  4  and 5 at the same time   pop doesn t accept multiple values  How else do I do this

User · Answer

If you can use numpy  then you can delete multiple indices    gt  gt  gt  import numpy as np  gt  gt  gt  a   np arange 10   gt  gt  gt  np delete a  1 3 5   array  0  2  4  6  7  8  9     and if you use np r  you can combine slices with individual indices    gt  gt  gt  np delete a  np r  0 5 7 9    array  5  6  8     However  the deletion is not in place  so you have to assign to it

User · Answer

There wasn t much hint on performance for the different ways so I performed a test on removing 5000 items from 50000 in all 3 generally different approaches  and for me numpy was the winner  if you have elements that fit in numpy     7 5 sec for the enumerated list comprehension  4 5 sec on another PC  0 08 sec for deleting items in reverse order  0 017     sec  0 009 sec for numpy delete  0 006 sec    Here s the code I timed  in the third function conversion from to list may be removed if working directly on numpy arrays is ok    import time import numpy as np import random  def del list indexes l  id to del       somelist    i for j  i in enumerate l  if j not in id to del      return somelist  def del list inplace l  id to del       for i in sorted id to del  reverse True           del l i    def del list numpy l  id to del       arr   np array l  dtype  int32       return list np delete arr  id to del    l   range 50000  random shuffle l  remove id   random sample range len l    5000    10     gt  5000

User · Answer

another option  in place  any combination of indices     marker   object    for i in indices      my list i     marker    marked for deletion  obj       v for v in my list if v is not  marker

User · Answer

If they re contiguous  you can just do   x 2 6         If you want to remove noncontiguous indexes  it s a little trickier   x    v for i v in enumerate x  if i not in frozenset  2 3 4 5

User · Answer

Old question  but I have an answer  First  peruse the elements of the list like so  for x in range len yourlist        print   s   s     x  yourlist x    Then  call this function with a list of the indexes of elements you want to pop   It s robust enough that the order of the list doesn t matter  def multipop yourlist  itemstopop       result          itemstopop sort       itemstopop   itemstopop   -1      for x in itemstopop          result append yourlist pop x       return result  As a bonus  result should only contain elements you wanted to remove   In  73   mylist     a   b   c   d   charles   In  76   for x in range len mylist          mylist x          0  a 1  b 2  c 3  d 4  charles     In  77   multipop mylist   0  2  4   Out 77     charles    c    a       In  78   mylist Out 78     b    d

User · Answer

You need to do this in a loop  there is no built-in operation to remove a number of indexes at once   Your example is actually a contiguous sequence of indexes  so you can do this   del my list 2 6    which removes the slice starting at 2 and ending just before 6   It isn t clear from your question whether in general you need to remove an arbitrary collection of indexes  or if it will always be a contiguous sequence   If you have an arbitrary collection of indexes  then   indexes    2  3  5  for index in sorted indexes  reverse True       del my list index    Note that you need to delete them in reverse order so that you don t throw off the subsequent indexes

User · Answer

remove indices    1 2 3  somelist    i for j  i in enumerate somelist  if j not in remove indices    Example   In  9   remove indices    1 2 3   In  10   somelist   range 10   In  11   somelist    i for j  i in enumerate somelist  if j not in remove indices   In  12   somelist Out 12    0  4  5  6  7  8  9

User · Answer

lst     a    b    c    d    e    f    g    lst   lst 0 2    lst 6     This is a single step operation  It  does not use a loop and therefore executes fast  It uses list slicing

[python] How to remove multiple indexes from a list at the same time?

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