CODEWITHSUNDEEP
pythonlistindexing
noobquestionsonly
noobquestionsonly

Reputation: 317

If the nth element of a list passes a condition, how do I select the nth element of another list?

If the nth element of pair_length passes a condition, then I want to write to an output file the nth elements of x_cords, y_cords, and pair_num. For example, if the 3rd element of the pair_length list passes the condition length <= average_pair_length():, then I want to select the 3rd elements of x_cords, y_cords, and pair_num lists so I can write them to an output file. I tried using the filter() function but it did not return what I wanted. Here is my code:

pair_length = []
pair_nums = []
x_cords = []
y_cords = []
for line in islice(data, 1, None):
    fields = line.split("   ")
    pair_num = float(fields[0])
    pair_nums.append(pair_num)
    x_cord = float(fields[1])
    x_cords.append(x_cord)
    y_cord = float(fields[2])
    y_cords.append(y_cord)
    vector_length = sqrt(x_cord**2 + y_cord**2)
    pair_length.append(vector_length)

def average_pair_length():
    average = mean(pair_length)
    return average

index = 0
for index, length in enumerate(pair_length):
    if length <= average_pair_length():
    #this is where I want to find the nth element of pair_length so I can find the nth elements in the other lists

Upvotes: 0

Views: 319

Answers (1)

Victor
Victor

Reputation: 2919

Use index to determine which element it is in the array

for index, length in enumerate(pair_length): # index tells you which element it is
    if length <= average_pair_length():
        x, y, pair_num = x_cords[index], y_cords[index], pair_nums[index]
        print(x, y, pair_num) 
        # Do what you want to do with the matching x, y, and pair_num here

Upvotes: 1

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