What does this: s[s[1:] == s[:-1]] do in numpy?

Question

I\'ve been looking for a way to efficiently check for duplicates in a numpy array and stumbled upon a question that contained an answer using this code.

What does th

Answer 1

It will show duplicates in a sorted array.

Basically, the inner expression s[1:] == s[:-1] compares the array with its shifted version. Imagine this:

1, [2, 3, ... n-1, n  ]
-  [1, 2, ... n-2, n-1] n
=> [F, F, ...   F, F  ]

In a sorted array, there will be no True in resulted array unless you had repetition. Then, this expression s[array] filters those which has True in the index array.