Array methods refactor

[nobu]

Array#sample

• Calculate statistics in Float. The expected average values should be real numbers. The currently selected values (iters and size) happen to be divisible in integer, but not in general.
• Move the invariant average value.
• Simplify counts array initializations.
• Simplify chi_squared calculations.
  • Use Array#sum.
  • Move the division by the invariant average outside the loop.

    Array#sort

• Adjust indents and add trailing commas.