Find the index of a dict within a list by matching the dict s value

Question

I have a list of dicts   list      id   1234   name   Jason              id   2345   name   Tom              id   3456   name   Art      How can I efficiently find the index position  0   1   or  2  by matching on name    Tom    If this were a one-dimensional list I could do list index   but I m not sure how to proceed by searching the values of the dicts within the list

User · Answer

For a given iterable  more itertools locate yields positions of items that satisfy a predicate   import more itertools as mit   iterable           id    1234    name    Jason          id    2345    name    Tom          id    3456    name    Art      list mit locate iterable  pred lambda d  d  name       Tom       1    more itertools is a third-party library that implements itertools recipes among other useful tools

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Here s a function that finds the dictionary s index position if it exists   dicts      id   1234   name   Jason               id   2345   name   Tom               id   3456   name   Art     def find index dicts  key  value       class Null  pass     for i  d in enumerate dicts           if d get key  Null     value              return i     else          raise ValueError  no dict with the key and value combination found    print find index dicts   name    Tom     1 find index dicts   name    Ensnare     ValueError  no dict with the key and value combination found

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I needed a more general solution to account for the possibility of multiple dictionaries in the list having the key value  and a straightforward implementation using list comprehension  dict indices    i for i  d in enumerate dict list  if d dict key     key value

User · Answer

Answer offered by  faham is a nice one-liner  but it doesn t return the index to the dictionary containing the value   Instead it returns the dictionary itself   Here is a simple way to get  A list of indexes one or more if there are more than one  or an empty list if there are none   list      id   1234   name   Jason              id   2345   name   Tom              id   3456   name   Art      i for i  d in enumerate list  if  Tom  in d values      Output    gt  gt  gt   1    What I like about this approach is that with a simple edit you can get a list of both the indexes and the dictionaries as tuples   This is the problem I needed to solve and found these answers   In the following  I added a duplicate value in a different dictionary to show how it works   list      id   1234   name   Jason              id   2345   name   Tom              id   3456   name   Art              id   4567   name   Tom       i  d  for i  d in enumerate list  if  Tom  in d values      Output    gt  gt  gt    1    id    2345    name    Tom      3    id    4567    name    Tom       This solution finds all dictionaries containing  Tom  in any of their values

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It won t be efficient  as you need to walk the list checking every item in it  O n    If you want efficiency  you can use dict of dicts   On the question  here s one possible way to find it  though  if you want to stick to this data structure  it s actually more efficient to use a generator as Brent Newey has written in the comments  see also tokland s answer     gt  gt  gt  L      id   1234   name   Jason                  id   2345   name   Tom                  id   3456   name   Art     gt  gt  gt   i for i   in enumerate L  if    name       Tom   0  1

User · Answer

A simple readable version is  def find lst  key  value       for i  dic in enumerate lst           if dic key     value              return i     return -1

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lst      id   1234   name   Jason      id   2345   name   Tom      id   3456   name   Art     tom index   next  index for  index  d  in enumerate lst  if d  quot name quot       quot Tom quot    None    1  If you need to fetch repeatedly from name  you should index them by name  using a dictionary   this way get operations would be O 1  time  An idea  def build dict seq  key       return dict  d key   dict d  index index   for  index  d  in enumerate seq    info by name   build dict lst  key  quot name quot   tom info   info by name get  quot Tom quot       index   1   id    2345    name    Tom

User · Answer

Seems most logical to use a filter index combo   names        name    Tom     name    Tony    names index filter lambda n  n get  name       Tom   names  0   1   And if you think there could be multiple matches    names index n  for item in filter lambda n  n get  name       Tom   names    1

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def search itemID list        return i for i in list if i itemID  itemID

User · Answer

One liner    elm     i for i in mylist if i  name       Tom   or  None   0

[python] Find the index of a dict within a list, by matching the dict's value

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