Question

I have two lists with values, the expected result is a tuple (a,b) where a is the number of i values which list1[i] < list2[i], and b is the number of i values where list1[i] > list2[i] (equalities are not counted at all).

I have this solution, and it works perfectly:

x = (0,0)
for i in range(len(J48)):
    if J48[i] < useAllAttributes7NN[i]:
      x = (x[0]+1,x[1])
    elif J48[i] > useAllAttributes7NN[i]:
        x = (x[0], x[1]+1)

However, I am trying to improve my python skills, and it seems very non-pythonic way to achieve it.

What is a pythonic way to achieve the same result?

FYI, this is done to achieve the required input for binom_test() that tries to prove two algorithms are not statistically identical.

I don’t believe this information has any additional value to the specific question though.

Answer 1

One way is to build a set of scores and then add them up.

scores = [ (a < b, a > b) for (a, b) in zip(J48, useAllAttributes7nn) ]
x = (sum( a for (a, _) in scores ), sum( b for (_, b) in scores ))

// Or, as per @agf's suggestion (though I prefer comprehensions to map)...
x = [ sum(s) for s in zip(*scores) ]

Another is to zip them once then count scores separately:

zipped = zip(J48, useAllAttributes7nn)
x = (sum( a < b for (a, b) in zipped ), sum( a > b for (a, b) in zipped ))

Note that this doesn’t work in Python 3 (thanks @Darthfett).