Anomaly Z-Score

Flag anomalies by z-score. Standardise x with its mean and population standard deviation (column-wise for a 2-D array) and mark every entry whose absolute z-score is strictly greater than threshold (default $33$). A constant column has z-score $00$ everywhere.

Implement solve(x, threshold=3).

Returns. Return a boolean NumPy array of the same shape as x.

Examples

Example 1

Input:

solve([1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 50.0], 2.5)

Output:

[False, False, False, False, False, False, False, False, False, True]

Example 2

Input:

solve([[1.0, 5.0], [2.0, 5.0], [3.0, 5.0]], 1.0)

Output:

[[True, False], [False, False], [True, False]]