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Python Introduction to NumPy Meet NumPy Multidimensional Arrays

Posted by Hailing Jin
Hailing Jin
363 Points

what does len(students_gpas) count? Is it the number of years on the first row or numbers of rows?

what does len(students_gpas) count? Is it the number of years on the first row or numbers of rows?If it is the number of years, then why do I get 3 instead of 4?

2 Answers

Boban Talevski
Boban Talevski
24,793 Points
Boban Talevski
Boban Talevski
24,793 Points

It is the number of rows indeed, which is why it returns 3. Technically, you ask how many elements this students_gpas array has? And it has 3 elements indeed. Each of them is another array each containing 4 elements, but len isn't concerned with that when it returns the result. It just sees 3 elements, it doesn't go deeper than that. 

import numpy as np
some_array = np.array([
    [1, 1, 1, 1, 1], # this is one element, who cares if it's a list or not, could be anything
    [1, 1, 1, 1, 1], # this is another, so 2 in total
])
len(some_array)

So in this case len(some_array) returns 2. Hope that makes things clearer.

Hailing Jin
Hailing Jin
363 Points

Thank you for the clear explanation! It really helped me so much!

ursaminor
ursaminor
11,271 Points
ursaminor
ursaminor
11,271 Points

I would guess it counts rows, but it's hard to know for sure without context. len() counts whatever iterable goes inside it. For example:

nums = [6, 3, 4, 77, 123]
len(nums) 
5

So what is students_gpas? That's your answer.

Hailing Jin
Hailing Jin
363 Points

Thank you!