I have a numpy array of 2000 elements and I want to find out the indexes in which the element minus the next element divided by itself is bigger than x.

Something like:

a[abs(a[i] - a[i 1])/a[i 1] > x]

I am looking for a way to do this by broadcasting instead of a for loop.

CodePudding user response：

You can use slicing. Start with the array including all but the last value (because the last one has no next value to compare it to), and index it with a Boolean expression: The same array, minus the shifted array starting at index 1, and divided by the shifted array. These operations will all happen element-wise in NumPy. Comparing with x gives the Boolean array that can be used as a filter:

a[:-1][np.abs(a[:-1] - a[1:]) / a[1:] > x]