iterating quickly through list of tuples

Question

I wonder whether there s a quicker and less time consuming way to iterate over a list of tuples  finding the right match  What I do is     this is a very long list  my list      old1  new1    old2  new2    old3  new3        oldN  newN      go through entire list and look for match for j in my list      if j 0     VALUE          PAIR FOUND   True         MATCHING VALUE   j 1          break   this code can take quite some time to execute  depending on the number of items in the list  I m sure there s a better way of doing this

User · Answer

I wonder whether the below method is what you want.

You can use defaultdict.

>>> from collections import defaultdict
>>> s = [('red',1), ('blue',2), ('red',3), ('blue',4), ('red',1), ('blue',4)]
>>> d = defaultdict(list)
>>> for k, v in s:
       d[k].append(v)    
>>> sorted(d.items())
[('blue', [2, 4, 4]), ('red', [1, 3, 1])]

User · Answer

I think that you can use   for j k in my list          stuff

User · Answer

The question is dead but still knowing one more way doesn t hurt   my list      old1  new1    old2  new2    old3  new3        oldN  newN    for first  args in my list      if first    Value          PAIR FOUND   True         MATCHING VALUE   args         break

User · Answer

Assuming a bit more memory usage is not a problem and if the first item of your tuple is hashable  you can create a dict out of your list of tuples and then looking up the value is as simple as looking up a key from the dict  Something like   dct   dict tuples  val   dct get key    None if item not found else the corresponding value   EDIT  To create a reverse mapping  use something like   revDct   dict  val  key  for  key  val  in tuples

User · Answer

The code can be cleaned up  but if you are using a list to store your tuples  any such lookup will be O N    If lookup speed is important  you should use a dict to store your tuples  The key should be the 0th element of your tuples  since that s what you re searching on  You can easily create a dict from your list   my dict   dict my list    Then   VALUE  my dict VALUE   will give you your matching tuple  assuming VALUE exists

[python] iterating quickly through list of tuples

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