Question

I have the following data structure:

data = [[{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '255', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '0', 'B': '255', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}],
        [{'Posit': '0', 'R': '0', 'B': '0', 'G': '255'}, {'Posit': '1000', 'R': '255', 'B': '0', 'G': '0'}]]

I want to find the most common list of dictionaries in the above data structure.

My first idea was to use the most_common function from collections.Counter, but

from collections import Counter
c = Counter()
for point in data:
    c[point] += 1

fails with a TypeError because lists are unhashable.

My next idea was to convert the list to a tuple because tuples are immutable

from collections import Counter
c = Counter()
for point in data:
    c[tuple(point)] += 1

but then I got a TypeError saying that dictionaries are also unhashable.

So what is a Pythonic way to accomplish what I want?

Answer 1

from collections import namedtuple, Counter
# You can probably think of a better name than this
datum = namedtuple('datum', 'Posit R B G')
Counter(tuple(datum(**d) for d in a) for a in data).most_common()
# You might actually want to make the conversion permanent;
# the data is possibly easier to work with that way given the
# fixed key structure, and it should save memory too