Overwriting an array in Numpy function Python

Question

I am trying to write a numpy function that iterates with itself to update the values of its function. If for example Random_numb was equal to [50, 74, 5, 69, 50]. So the calculations would go like, 10* 50 = 500 for the first calculation, with the equation Starting_val = Starting_val * Random_numb. The Starting_Val would equal to 500 so for the second calculation it would go as 500 * 74 = 37000. Updating the Startin_Val to 37000 from 500. Iterating through the Random_numb as it does the calculations, using element 1: 50 for calculation 1 and element 2 74 for calculation 2 and so on. The calculations would go on until the end of the Random_numb array.

import numpy as np
Starting_val = 10
Random_numb = random.randint(100, size=(5))
Starting_val = Starting_val * Random_numb

Stef · Accepted Answer · 2021-02-07 12:56:01Z

1

IIUC you're looking for prod:

import numpy as np

Starting_val = 10
Random_numb = np.array([50, 74, 5, 69, 50])

Random_numb.prod(initial=Starting_val)
#638250000

If you're interested in the multiplied values of the array it'll be cumprod:

Starting_val * Random_numb.cumprod()
# array([      500,     37000,    185000,  12765000, 638250000])

edited Feb 7, 2021 at 12:56

answered Feb 7, 2021 at 12:33

Stef

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3 Comments

tony selcuk Over a year ago

Thank is there a way I could perform more advanced arithmetic's with multipication division and addition like Starting_val = Starting_val + Starting_val * Random_numb/10

Stef Over a year ago

what do you need in the end: just one value (like in prod above) or the whole array (like in cumprod)? It would be best you provide the desired output for the example.

tony selcuk Over a year ago

I have posted a new question about it I would appreciate it If you could take a look and perhaps it is more clear. stackoverflow.com/questions/66091981/…

Ashish Jain · Accepted Answer · 2021-02-07 06:22:16Z

1

Here you are just multiplying the Starting_val with your array of random numbers. You are not updating Starting_val each time. Try out the below code

for i in range(len(Random_numb)):
    Random_numb[i] *= Starting_val
    Starting_val = Random_numb[i]

Hope this solves your query!

answered Feb 7, 2021 at 6:22

Ashish Jain

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1 Comment

tony selcuk Over a year ago

I am trying not to use for loops and use numpy instead as it is much faster, but thank you.

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