Is there a method to multiply only certain elements in a numpy array [duplicate]

Question

Suppose I have a numpy array like so:

a = ([[4, 9], [38, 8], [90, 10]...[8545, 17]])

Where the first element is a location ID and the second is the amount of time spent at each location in minutes. I want to convert these times into seconds which requires me to multiply every other value by 60.

As this is a very long array, what would be the most time-efficient method for converting these times?

swag2198 · Accepted Answer · 2021-04-13 18:45:25Z

2

Use this:

import numpy as np
# a is your original list of [location, time] pairs
a = np.array(a)
a[:, 1] *= 60

It simply multiplies the second column of your array a by 60 to convert the time values into seconds.

edited Apr 13, 2021 at 18:45

answered Apr 13, 2021 at 11:36

swag2198

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3 Comments

RevolverOshawott Over a year ago

Thank you, much simpler than the for loop I was trying to use

Mad Physicist Over a year ago

You'd be better off using a[:, 1] *= 60. It's an in-place operation and won't allocate a temp array.

swag2198 Over a year ago

@Mad Physicist: Thanks for the comment. Noted.

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