Counting the most common element in a 2D List in Python

Question

I am looking for a way to count occurency in a 2D List. For example I have a list like that:

[[John, 3],[Chris, 3],[Bryan,5],[John,3],[John,7]]

As an output I want to count which numbers does John have most common like that

Most common number for the John is: 3

I did it for all the names easily with

Counter(my_list[1]).most_common(5)

Does anyone have a suggestion to do it?

Answer 1

This should work.

from collections import Counter
main_list = [['John', 3],['Chris', 3],['Bryan',5],['John',3],['John',7]] #your_list
new_list = [i[1] for i in main_list if i[0]=='John']
print(Counter(new_list).most_common(1)[0][0])

Answer 2

I would probably re-shape the input data before doing queries on it. Maybe name vs values:

name_lookup = defaultdict(list)
for name, value in my_list:
    name_lookup[name].append(value)

name = 'John'
most_common, _ = Counter(name_lookup[name]).most_common(1)[0]
print(f"Most common number for {name} is: {most_common}")

Answer 3

You could also do filtering and mapping:

my_list = [['John', 3],['Chris', 3],['Bryan',5],['John',3],['John',7]]

print(Counter(map(lambda y: y[1], filter(lambda x: x[0] == "John", my_list))).most_common(1))

Answer 4

If you are 100% sure that there always will be exactly 1 most-frequent element for each name, you migth sort by name, groupby by name and then use statistics.mode following way:

import itertools
import statistics
some_data = [['John', 3],['Chris', 3],['Bryan',5],['John',3],['John',7]]
sorted_data = sorted(some_data,key=lambda x:x[0]) # sort by name
most_frequent = {name:statistics.mode(j[-1] for j in list(data)) for name,data in itertools.groupby(sorted_data,key=lambda x:x[0])}
print(most_frequent) # {'Bryan': 5, 'Chris': 3, 'John': 3}

itertools.groupby returns pairs of name-data, but as data s itself contain both key (name in our case) and value (number in our case) we need comprehension to get "raw" values.