CODEWITHSUNDEEP
pythonoptimization
Suat Atan PhD
Suat Atan PhD

Reputation: 1382

Selecting Pareto-Dominant Vector

I want to compare two vector. This vector represents two alternative:

def select_dominant(a,b):
    comp=a>b
    if(comp):
        return a
    elif(a<b):
        return b
    else:
        return "indifferent"

a=[1,10,1]
b=[1,1,10]
print(select_dominant(a,b))

It's expected that a and b should be "indifferent" because a and b can't dominate each other. For values like a=[1,1,1] b=[1,1,2] there is no problem for this code because b dominated to a. Consequently, i want to get "indifferent" return from this function. How can i get?

Upvotes: 2

Views: 561

Answers (1)

unutbu
unutbu

Reputation: 879481

It looks like you want to compare two lists elementwise. If all the values in a are greater than or equal to the corresponding values in b, then return a, if less than or equal return b, and otherwise return 'indifferent'.

You can apply the >= operator to each element of a and b like this:

In [247]: a = [1,10,1]

In [248]: b = [1,1,10]

In [249]: map(operator.ge, a, b)
Out[249]: [True, True, False]

And you can test if all the values are True using all:

In [250]: all(map(operator.ge, a, b))
Out[250]: False

Thus, if you define:

import operator
def select_dominant(a,b):
    ge = all(map(operator.ge, a, b))
    le = all(map(operator.le, a, b))
    return a if ge else b if le else 'indifferent'

then

In [242]: select_dominant([1,1,1], [1,1,2])
Out[242]: [1, 1, 2]

In [243]: select_dominant([1,1,2], [1,1,1])
Out[243]: [1, 1, 2]

In [244]: select_dominant([1,10,1], [1,1,10])
Out[244]: 'indifferent'

The expression

a if ge else b if le else 'indifferent'

is a so-called conditional expression. It is a short-hand way to generate the same value that this code would assign to value:

if ge:
    value = a
elif le:
    value = b
else:
    value = 'indifferent'

Upvotes: 4

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