Find number of consecutive elements that are the same before they change

Question

So for example if I have the lists

a = [1,1,1,2,2]
b = [1,1,2,2,2]
c = [2,1,1,1,1]

I would want to get the longest streak of the first element in the list, so for example a would give 3, b would give 2 and c would give 1. I know I could create a while loop and count the streak that way, but I was wondering if there's a more elegant way to do this?

Answer 1

you could do something like this:

numStreak = ([a[0] == n for n in a]+[False]).index(False)

(this also makes sure that if all elements are like the first element, index does return the correct value)

UPDATE: a more efficient (but less elegant?) version

from itertools import takewhile
len([1 for _ in takewhile(lambda x:x==a[0], a)])

or a bit better (UPDATE 2) @vaultah's suggestion:

sum(1 for _ in takewhile(lambda x:x==a[0], a))