Group list by values

python list grouping
Veles picture Veles · Apr 17, 2011 · Viewed 133.3k times · Source

Let's say I have a list like this:

mylist = [["A",0], ["B",1], ["C",0], ["D",2], ["E",2]]

How can I most elegantly group this to get this list output in Python:

[["A", "C"], ["B"], ["D", "E"]]

So the values are grouped by the secound value but the order is preserved...

Answer

Howard picture Howard · Apr 17, 2011 
values = set(map(lambda x:x[1], mylist))
newlist = [[y[0] for y in mylist if y[1]==x] for x in values]

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