How to compare two dicts based on roundoff values in python?

Question

I need to check if two dicts are equal. If the values rounded off to 6 decimal places are equal, then the program must say that they are equal. For e.g. the following two dicts are equal

{'A': 0.00025037208557341116}

and

{'A': 0.000250372085573415}

Can anyone suggest me how to do this? My dictionaries are big (more than 8000 entries) and I need to access this values multiple times to do other calculations.

Yes, actually I compute a dict iteratively and I need to stop the iteration if the current dict is same as the old one. — user1219801, Nov 24 '12 at 12:47
And what if it is different? I'd compare *each* key and value as you compute the dict. Looking up the key/value pair as you go along computing the other dict is relatively cheap (linear time). — Martijn Pieters, Nov 24 '12 at 12:49
If they are different, computation should go on. Since my dict is big, I was thinking to find another way of comparing the dicts instead of looking up the dict entries during computation. — user1219801, Nov 24 '12 at 12:53
But you can stop comparing from that point onwards, since they will never be the same as soon as you find your first difference. — Martijn Pieters, Nov 24 '12 at 12:57

score 0 · Accepted Answer · edited May 23 '17 at 12:18

Test each key as you produce the second dict iteratively. Looking up a key/value pair from the dict you are comparing with is cheap (linear cost), and round the values as you find them.

You are essentially performing a set difference to test for equality of the keys, which requires at least a full loop over the smallest of the sets. If you already need to loop to generate one of the dicts, you are at an advantage as that'll give you the shortest route to determining inequality soonest.

To test for two floats being the same within a set tolerance, see What is the best way to compare floats for almost-equality in Python?.

How to compare two dicts based on roundoff values in python?

1 Answers1