Peaks are the points that are surrounded by smaller value points on either side as shown in the image below:

There are two ways of finding local maxima:

Using .where() method: This method lists all positions/indices where the element value at position i is greater than the element on either side of it. This method does not check for the points that have only one neighbour. This is demonstrated in the example below:

Output:

• The +1 at the end of the expression is required as it finds the indexes within the slice arr[1:-1] and not the entire array arr.


• The where() method returns a tuple of arrays where the first element is our required array. Hence we add [0] after the where method.

Using combination of .diff(), .sign() and .where() method:

• In this method, we calculate the difference between each element using the diff() method of NumPy.


• Then we use the sign() method on the array to get the sign of difference.


• The value can be either -1 or +1. This result is then passed on to another diff() method which returns 0, -2 or +2 value. The value 0 indicates that the points are continuously increasing or decreasing, +2 indicates minimum peak and -2 indicates maximum peak (local maxima).


• We then identify the position or indexes of the local maxima using the where() method. The reason for using +1 at the end of where and [0] after where is the same as the explanation described in Method 1 for finding local maxima.

The following code example demonstrates this:

Output: