Python: use of Counter in a dictionary of lists

Question

Given a dictionary of lists like this: d={0:[0.1,0.2,0.1], 1:[1.1,1.2,0.1], 2:[2.1,2.2,0.1]}

I want to be able to count how many times each individual value appears in all lists. In the example given, the intended outcome would be:

occurrences={0.1:4, 0.2:1, 1.1:1, 1.2:1, 2.1:1, 2.2:1}

I was thinking of using Counter in a line like this:

occurrences = Counter([k[0] for k in d.values()])

but the output is Counter({0.1: 1, 1.1: 1, 2.1: 1}), meaning that the previous line only counts the occurrences of the first element of each list.

How can I extend this count to all elements of all lists?

Are the elements in your lists floats? If so, you are going to need to define a tolerance in order to get meaningful results. — Chris Mueller
– Chris Mueller, Commented Oct 25, 2016 at 15:12

Graham · Accepted Answer · 2017-09-27 04:08:27Z

6

Since you don't appear to care about the keys of the dict, you can just use a comprehension:

>>> Counter(v for sublist in d.values() for v in sublist)
Counter({0.1: 4, 0.2: 1, 1.1: 1, 1.2: 1, 2.1: 1, 2.2: 1})

edited Sep 27, 2017 at 4:08

Graham

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answered Oct 25, 2016 at 15:12

wim

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Moses Koledoye · Accepted Answer · 2016-10-25 15:13:24Z

3

You need to put all the value lists in one flat list and then count. You can pass the dictionary's list of values to itertools.chain.from_iterable to flatten them:

from collections import Counter
from itertools import chain

d={0:[0.1,0.2,0.1], 1:[1.1,1.2,0.1], 2:[2.1,2.2,0.1]}
c = Counter(chain.from_iterable(d.values()))
print(c)
# Counter({0.1: 4, 0.2: 1, 1.2: 1, 2.2: 1, 1.1: 1, 2.1: 1})

answered Oct 25, 2016 at 15:13

Moses Koledoye

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