python tip

If we need to count the number of elements in a list, there is a very handy tool in the collections module that does exactly this. We just need to import the Counter from collections, and then create our counter object with the list as argument. If we print this, then for each item in our list we see the according number of times that this item appears, and it's also already sorted with the most common item being in front. This is much nicer to calculate it on our own. If we the want to get the count for a certain item, we can simply access this item, and it will return the corresponding count. If the item is not included, then it returns 0.

from collections import Counter

my_list = [10, 10, 10, 5, 5, 2, 9, 9, 9, 9, 9, 9]
counter = Counter(my_list)

print(counter) # Counter({9: 6, 10: 3, 5: 2, 2: 1})
print(counter[10]) # 3

It also has a very handy method to return the most common items, which - no surprise - is called most_common(). We can specify if we just want the very most common item, or also the second most and so on by passing in a number. Note that this returns a list of tuples. Each tuple has the value as first value and the count as second value. So if we just want to have the value of the very most common item, we call this method and then we access index 0 in our list (this returns the first tuple) and then again access index 0 to get the value.

from collections import Counter

my_list = [10, 10, 10, 5, 5, 2, 9, 9, 9, 9, 9, 9]
counter = Counter(my_list)

most_common = counter.most_common(2)
print(most_common) # [(9, 6), (10, 3)]
print(most_common[0]) # (9, 6)
print(most_common[0][0]) # 9