Iterate In 2 Different Dictionaries Simultaneously In Python

---EDIT 2--- So I get the question Why I use dictionaries?, this question is a follow up on this one: csv file compression without using existing libraries in Python I Need to com

Solution 1:

So first of all you want to reverse the mapping, you are currently looking by value, which is wrong and slow:

ticks = {0: '6NH8', 1: '6AH8', 2: 'QMH8'}
symbs = {0: 'F,A', 1: 'F,B'}

Using ticks = {v: k for k, v in ticks.items()} (same for symbs):

{'6NH8': 0, 'QMH8': 2, '6AH8': 1} # ticks

{'F,A': 0, 'F,B': 1} # symbs

Now that you have good data structures you can do this rather fast.

Now transform the dictionary that holds the data to a list (not sure why it is a dictionary to start with):

originalList = [originalDict[k] for k in range(len(originalDict))]

And re-map values:

for line in originalList:
    line[0] = ticks[line[0]]
    line[1:3] = [symbs["%s,%s" % tuple(line[1:3])]]

result:

[[0, 0, '0', '60541567', '60541567', '78.78', '20'], [0, 0, '0', '60541569', '60541569', '78.78', '25'], [1, 1, '0', '60541765', '60541765', '90.52', '1'], [2, 1, '0', '60437395', '60437395', '950.5', '1']]

Solution 2:

You can speed up the lookup by inverting the keys and values in the ticks and symbs dicts and then just looking up the right values instead of iterating and comparing all the values in the dicts:

ticks_inv = {v: k for k, v in ticks.items()}
symbs_inv = {v: k for k, v in symbs.items()}

forvalues in originalDict.values():
    ifvalues[0] in ticks_inv:
        values[0] = ticks_inv[values[0]]

    comprComb = "{v[1]},{v[2]}".format(v=values)
    if comprComb in symbs_inv:
        values[1] = symbs_inv[comprComb]
        del values[2]

Result is the same as with your code, but should be much faster, particularly if ticks and symbs are large. Of course, this assumes that the values are unique, but if otherwise your code would not work correctly ether.

Solution 3:

Your dictionary is backwards; it's not using the dictionary's key-lookup feature. Instead of

for ticksKey, ticksValue in ticks.items():
    ifvalues[0] == ticksValue:
        values[0] = ticksKey

try

ticks = {'6NH8': 0, '6AH8': 1, 'QMH8': 2}
...
ifvalues[0] in ticks:
    values[0] = ticks[values[0]]

A little weirder looking would be just

values[0] = ticks[values[0]] orvalues[0]

If you do that, and similarly with symbs, you'll remove all but the necessary outmost loop and see a significant performance improvement.