d3.piecewise?

[mbostock]

A very lightweight piecewise linear scale. Implementation:

d3.piecewise = function(interpolate, values) {
  var n = values.length - 1, I = d3.pairs(values, interpolate);
  return function(t) {
    var i = Math.max(0, Math.min(n - 1, Math.floor(t *= n)));
    return I[i](t - i);
  };
};

Example usage:

d3.piecewise(d3.interpolateRgb, ["red", "green", "blue"])

[mbostock]

Compared to d3-scale:

d3.scaleLinear()
    .domain([0, 0.5, 1])
    .range(["red", "green", "blue"])
    .interpolate(d3.interpolateRgb)

[mbostock]

Added in #55.