Using Python s list index method on a list of tuples or objects

Question

Python s list type has an index   method that takes one parameter and returns the index of the first item in the list matching the parameter   For instance    gt  gt  gt  some list     apple    pear    banana    grape    gt  gt  gt  some list index  pear   1  gt  gt  gt  some list index  grape   3   Is there a graceful  idiomatic  way to extend this to lists of complex objects  like tuples   Ideally  I d like to be able to do something like this    gt  gt  gt  tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    gt  gt  gt  some list getIndexOfTuple 1  7  1  gt  gt  gt  some list getIndexOfTuple 0   kumquat   2   getIndexOfTuple   is just a hypothetical method that accepts a sub-index and a value  and then returns the index of the list item with the given value at that sub-index   I hope  Is there some way to achieve that general result  using list comprehensions or lambas or something  in-line  like that   I think I could write my own class and method  but I don t want to reinvent the wheel if Python already has a way to do it

User · Answer

Those list comprehensions are messy after a while   I like this Pythonic approach   from operator import itemgetter  def collect l  index      return map itemgetter index   l     And now you can write this  collect tuple list 0  index  cherry         1 collect tuple list 1  index  3              2   If you need your code to be all super performant     Stops iterating through the list as soon as it finds the value def getIndexOfTuple l  index  value       for pos t in enumerate l           if t index     value              return pos        Matches behavior of list index     raise ValueError  list index x   x not in list    getIndexOfTuple tuple list  0   cherry         1

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tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    def eachtuple tupple  pos1  val       for e in tupple          if e    val              return True  for e in tuple list      if eachtuple e  1  7  is True          print tuple list index e   for e in tuple list      if eachtuple e  0   kumquat   is True          print tuple list index e

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z   list zip  tuple list   z 1  z 0  index  persimon

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How about this    gt  gt  gt  tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    gt  gt  gt   x for x  y in enumerate tuple list  if y 1     7   1   gt  gt  gt   x for x  y in enumerate tuple list  if y 0      kumquat    2    As pointed out in the comments  this would get all matches  To just get the first one  you can do    gt  gt  gt   y 0  for y in tuple list  index  kumquat   2   There is a good discussion in the comments as to the speed difference between all the solutions posted  I may be a little biased but I would personally stick to a one-liner as the speed we re talking about is pretty insignificant versus creating functions and importing modules for this problem  but if you are planning on doing this to a very large amount of elements you might want to look at the other answers provided  as they are faster than what I provided

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No body suggest lambdas   Y try this and works  I come to this post searching answer  I don t found that  I like  but I feel a insingth  P      l     rana   1  1     pato   1  1     perro   1  1        map lambda x x 0   l  index  pato    1    Edit to add examples       l    rana   1  1     pato   2  1     perro   1  1     pato   2  2     pato   2  2     extract all items by condition          filter lambda x x 0    pato   l      pato   2  1     pato   2  2     pato   2  2    extract all items by condition with index        gt  gt  gt  filter lambda x x 1  0    pato   enumerate l         1    pato   2  1     3    pato   2  2     4    pato   2  2         gt  gt  gt  map lambda x x 1            pato   2  1     pato   2  2     pato   2  2     Note   variable only works in interactive interpreter y normal text file   need explicti assign  ie   filter lambda x x 1  0    pato   enumerate l

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ok  it might be a mistake in vals j   the correction is   def getIndex li indices vals   for pos k in enumerate lista       match   True     for i in indices          if k i     vals indices index i                match   False             break     if match           return pos

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I would place this as a comment to Triptych  but I can t comment yet due to lack of rating   Using the enumerator method to match on sub-indices in a list of tuples  e g   li     1 2 3 4    11 22 33 44    111 222 333 444     a   b   c   d              aa   bb   cc   dd      aaa   bbb   ccc   ddd       want pos of item having  22 44  in positions 1 and 3   def getIndexOfTupleWithIndices li  indices  vals          if index is a tuple of subindices to match against      for pos k in enumerate li           match   True         for i in indices              if k i     vals i                   match   False                 break          if  match               return pos        Matches behavior of list index     raise ValueError  list index x   x not in list    idx    1 3  vals    22 44  print getIndexOfTupleWithIndices li idx vals         1 idx    0 1  vals     a   b   print getIndexOfTupleWithIndices li idx vals         3 idx    2 1  vals     cc   bb   print getIndexOfTupleWithIndices li idx vals         4

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Python s list index x  returns index of the first occurrence of x in the list  So we can pass objects returned by list compression to get their index    gt  gt  gt  tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    gt  gt  gt   tuple list index t  for t in tuple list if t 1     7   1   gt  gt  gt   tuple list index t  for t in tuple list if t 0      kumquat    2    With the same line  we can also get the list of index in case there are multiple matched elements    gt  gt  gt  tuple list      pineapple   5     cherry   7     kumquat   3     plum   11     banana   7    gt  gt  gt   tuple list index t  for t in tuple list if t 1     7   1  4

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Inspired by this question  I found this quite elegant    gt  gt  gt  tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    gt  gt  gt  next i for i  t in enumerate tuple list  if t 1     7  1  gt  gt  gt  next i for i  t in enumerate tuple list  if t 0      kumquat   2

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You can do this with a list comprehension and index    tuple list      pineapple   5     cherry   7     kumquat   3     plum   11    x 0  for x in tuple list  index  kumquat   2  x 1  for x in tuple list  index 7  1

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I guess the following is not the best way to do it  speed and elegance concerns  but well  it could help     from collections import OrderedDict as od t      pineapple   5     cherry   7     kumquat   3     plum   11   list od t  keys    index  kumquat   2 list od t  values    index 7  7   bonus   od t   kumquat   3   list of tuples with 2 members can be converted to ordered dict directly  data structures are actually the same  so we can use dict method on the fly

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One possibility is to use the itemgetter function from the operator module   import operator  f   operator itemgetter 0  print map f  tuple list  index  cherry     yields 1   The call to itemgetter returns a function that will do the equivalent of foo 0  for anything passed to it  Using map  you then apply that function to each tuple  extracting the info into a new list  on which you then call index as normal   map f  tuple list    is equivalent to    f tuple list 0    f tuple list 1       etc    which in turn is equivalent to    tuple list 0  0   tuple list 1  0   tuple list 2  0     which gives     pineapple    cherry      etc

[python] Using Python's list index() method on a list of tuples or objects?

I like this Pythonic approach:

If you need your code to be all super performant:

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