[SOLVED] How to retain the index of an array element after flattening and sorting into descending order using sort()

How to retain the index of an array element after flattening and sorting into descending order using sort()

I have a 2D array of integers. I need to find the largest value within the entire array along with its index.

Currently I am flattening the array and then using the sort() function to find the highest value. The problem is my array has multiples (12,000,000+ elements) so after sorting I don't know how to recover the index.

maskingarray = Data.copy()
flatmask = maskingarray.flatten()
flatmask.sort()

This code allows me to access the element with the highest value but I need but the position in the 2D array also.

Is there a better method which allows me to retain the indexing of the original array? Preferably just finding the largest value without having to flatten at all.

(For context: I need the indexing because I am doing aperture photometry, essentially finding a galaxy with the highest luminosity and looking at a radius around it)

Thanks for any help

Solution

This is similar to prior questions, and I think the answer is in [this one][1] https://stackoverflow.com/questions/5469286/how-to-get-the-index-of-a-maximum-element-in-a-numpy-array-along-one-axis

There is an elegant solution using Numpy [argmax][1] [1]: https://numpy.org/doc/stable/reference/generated/numpy.argmax.html

an argmax solution:

>>> import numpy as np
>>> a = np.array([[1,2,3],[4,3,1]])
>>> i,j = np.unravel_index(a.argmax(), a.shape)
>>> [i,j]
[1,0]
>>> a[i,j]
4