ruby - How do I map number ranges to each other? -

how can map 2 opposing numbers ranges each other?

i have 1 range 3 numbers: 1, 2, 3 (and potential decimals).

i'd map on range of 1000 0.

so, 1 = 1000, 2 = 500, 3 = 0.

ultimately, want take number 1.68 , figure out on 1000-0 scale it'd match up.

using math!

assuming want linear mapping first range (1-3) second (1000-0, descending), function:

y = (3 - x) / 2 * 1000 

where x input (1 <= x <= 3) , y output (0 <= y <= 1000).

this can generalized different ranges needed.

patent pending.