How can we count text 'changes' in a list?-CodePudding

How can we count text 'changes' in a list?

The list below has 0 'changes'. Everything is the same.

['Comcast', 'Comcast', 'Comcast', 'Comcast', 'Comcast', 'Comcast']

The list below has 3 changes. First change is Comcast>Sprint, second change is Sprint>AT&T and third change is AT&T>Comcast.

['Comcast', 'Comcast', 'Sprint', 'AT&T', 'Comcast', 'Comcast']

I Googled this before posting here. Finding unique items seems pretty easy. Finding changes, or switches, seems not so easy.

CodePudding user response：

One option is to use itertools.groupby. This counts the number of "chunks" and subtract one (to get the "boundaries").

from itertools import groupby

lst = ['Comcast', 'Comcast', 'Sprint', 'AT&T', 'Comcast', 'Comcast']

output = sum(1 for _ in groupby(lst)) - 1
print(output) # 3

CodePudding user response：

You want to compare elements pairwise, so you can create an iterator to pair up adjacent elements:

>>> l = [ 1, 1, 2, 3, 1, 1, 1, ]
>>> list(zip(l[:-1], l[1:]))
[(1, 1), (1, 2), (2, 3), (3, 1), (1, 1), (1, 1)]

Then iterate over them and test if they're pairwise equal:

>>> [x == y for (x, y) in zip(l[0:-1], l[1:])]
[True, False, False, False, True, True]

Then count them where they are not equal:

>>> sum(1 for (x, y) in zip(l[0:-1], l[1:]) if x != y)
3