How to count number of distinct entries in 2d list?

Question

I have a 2D list and I want to learn how to return the number of distinct entries there are in the table.

numbers = [[32, 12, 52, 63], [32, 64, 67, 52], [64,64,17,34], [17, 76, 98]]

since there are 10 numbers that are not the same I want it to return that number, how do I go about that?

Answer 1

Convert your nested list into a set and take the length of it, as below:

numbers = [[32, 12, 52, 63], [32, 64, 67, 52], [64,64,17,34], [17, 76, 98]]

numbers_set = set(i for j in numbers for i in j)
print(len(numbers_set)) # 10

Sets are containers with no duplicate elements, this means that set([1, 1, 2]) -> {1, 2}. The length of the set can then be used to find the number of distinct values originally in your nested lists.

Answer 2

Flatten the list in a set comprehension to remove the dups

print len({x for y in numbers for x in y})
10

Or create a set and use set.update:

s = set()

s.update(*numbers)
print len(s)
10


In [1]: numbers = [[32, 12, 52, 63], [32, 64, 67, 52], [64,64,17,34], [17, 76, 98]]

In [2]: s = set()

In [3]: s.update(*numbers)

In [4]: s
Out[4]: {12, 17, 32, 34, 52, 63, 64, 67, 76, 98}

python sets