Iterating two arrays in python with two different conditions

Question

How do I iterate two sets of array with two different conditions? I am using iris data and trying to classify if it is versicolour or vigrinica.

array = dataframe.values
petalLength = array[50:,2]
petalWidth = array[50:,3]

I'm trying to iterate two arrays, but not getting the results I need.

def decision(petalLength, petalWidth):
    for x in petalLength:
        for y in petalWidth:
            if x < 4.8 and y < 1.8:
                print("Versicolour")
            else:
                print("Virginica")

Results for example:

petal Length is 4.7 and petal Width is 1.5 the answer should be Versicolour
petal Length is 4.7 and petal width is 1.9 the answer should be Virginica

score 1 · Answer 1 · answered Oct 22 '18 at 06:24

1

I assume what you want is pair-wise iteration, which you would generally do with zip:

for x, y in zip(petalLength, petalWidth):
    if x < 4.8 and y < 1.8:
        print("Versicolour")
    else:
        print("Virginica")

answered Oct 22 '18 at 06:24

user2390182

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score 0 · Answer 2 · answered Oct 22 '18 at 06:26

You have nested for loops which gives you N^2 results, when you only want to do the operation once.

Every inner loop is run len(petalLength) times... Which compares every petalWidth to every petalLength instead of doing it in pairs.

def decision(petalLength, petalWidth):
    for i in range(len(petalLength)):
        if petalLength[i] < 4.8 and petalWidth[i] < 1.8:
            print("Versicolour")
        else:
            print("Virginica")

Thanks for the explanation; it really helps! – Limzilla Oct 22 '18 at 15:04 — Limzilla, Oct 22 '18 at 15:04

score 0 · Answer 3 · answered Oct 22 '18 at 06:28

Addition to schwobaseggl's answer, use return instead of print:

def decision(petalLength, petalWidth):
    for x, y in zip(petalLength, petalWidth):
        if x < 4.8 and y < 1.8:
            return "Versicolour"
        else:
            return "Virginica"

Then now:

print(decision(petalLength,petalWidth))

Will return as desired output,

But previously, it will output desired output, then an other line having None

Same with Aleksei Maide's answer.

Iterating two arrays in python with two different conditions

3 Answers3