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 lon         


        

Answer 1

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)

Answer 2

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

Answer 3

I think that you can use

for j,k in my_list:
  [ ... stuff ... ]

Answer 4

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).

Answer 5

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])]