finding the position of an element within a numpy array in python [duplicate]

Question

I want to ask a question about finding the position of an element within an array in Python's numpy package.

I am using Jupyter Notebook for Python 3 and have the following code illustrated below:

concentration_list = array([172.95, 173.97, 208.95])

and I want to write a block of code that would be able to return the position of an element within the array.

For this purpose, I wanted to use 172.95 to demonstrate.

Initially, I attempted to use .index(), passing in 172.95 inside the parentheses but this did not work as numpy does not recognise the .index() method -

concentration_position = concentration_list.index(172.95)

AttributeError: 'numpy.ndarray' object has no attribute 'index'

The Sci.py documentation did not mention anything about such a method being available when I accessed the site.

Is there any function available (that I may not have discovered) to solve the problem?

Answer 1

You can go through the where function from the numpy library

import numpy as np

concentration_list = np.array([172.95, 173.97, 208.95])
number = 172.95

print(np.where(concentration_list == number)[0])


Output : [0]

Answer 2

Use np.where(...) for this purpose e.g.

import numpy as np

concentration_list = np.array([172.95, 173.97, 208.95])

index=np.ravel(np.asarray(concentration_list==172.95).nonzero())

print(index)

#outputs (array of all indexes matching the condition):

>> [0]