make-range-transform.js

import clamp from 'lodash/fp/clamp'
import compose from 'lodash/fp/compose'

// Create an affine transformation to map numbers from one range to another.
export function makeRangeTransform({
    domain: [minX, maxX],
    range: [minY, maxY],
    clampOutput = false,
}) {
    const scale = (maxY - minY) / (maxX - minX)
    const bias = minY - minX * scale
    const transform = x => bias + x * scale
    return clampOutput ? compose(clamp(minY, maxY), transform) : transform
}

// Create a transformation that passes the input through a monotonic nonlinearity
export function makeNonlinearTransform({
    domain,
    range,
    nonlinearity,
    clampOutput = false,
}) {
    return function nonLinearTransform(input) {
        const toOutputRange = makeRangeTransform({
            domain: domain.map(nonlinearity),
            range,
            clampOutput,
        })
        return toOutputRange(nonlinearity(input))
    }
}