How to find first element in sorted numpy array that is smaller than a given scalar

Also see How to find first element in sorted numpy array that is larger than a given scalar

You can use np.searchsorted() like this:

idx = np.searchsorted(arr, scalar, side='left')

Full example:

import numpy as np

# Example array
arr = np.array([1, 2, 3, 4, 5])

# We'll search for this value
scalar = 3.5

# Use numpy.searchsorted() to find the first element in the array that is smaller than the scalar
idx = np.searchsorted(arr, scalar, side='left')

# Print the resulting index
print(idx)