I want to know which would be an efficient method to invert dictionaries in python. I also want to get rid of duplicate values by comparing the keys and choosing the larger over the smaller assuming they can be compared. Here is inverting a dictionary:
inverted = dict([[v,k] for k,v in d.items()]) To remove duplicates by using the largest key, sort your dictionary iterator by value. The call to dict will use the last key inserted:
import operator inverted = dict((v,k) for k,v in sorted(d.iteritems(), key=operator.itemgetter(1))) Here is a simple and direct implementation of inverting a dictionary and keeping the larger of any duplicate values:
inverted = {} for k, v in d.iteritems(): if v in inverted: inverted[v] = max(inverted[v], k) else: inverted[v] = k This can be tightened-up a bit with dict.get():
inverted = {} for k, v in d.iteritems(): inverted[v] = max(inverted.get(v, k), k) This code makes fewer comparisons and uses less memory than an approach using sorted().
