Function percentRank

Percentage of period previous values less than or equal to the current subject, excluding the subject itself. Omitted options preserve legacy behavior. Supplied skip collects previous finite observations; propagate requires a full previous chronological window. A missing subject or insufficient history produces NaN under either policy. Equality counts. Invalid option-path periods throw RangeError; malformed policies throw TypeError. Periods must be positive safe integers.

Bar-aligned lengths count previous observations. A missing current subject or length gives NaN.