Gini impurity classifier

[kosiarn]

Write a Gini impurity function that given discrete value vector calculates its' Gini impurity value.

Example 1:

• Input: [1, 1, 0, 1, 0]
• Output: 0.4800
  Example 2:
• Input: [1, 1, 1, 1]
• Output: 0.0000