d3.scale.quantile = function() {

  return d3_scale_quantile([], []);

};

function d3_scale_quantile(domain, range) {

  var thresholds;

  function rescale() {

    var k = 0,

        n = domain.length,

        q = range.length;

    thresholds = [];

    while (++k < q) thresholds[k - 1] = d3.quantile(domain, k / q);

    return scale;

  }

  function scale(x) {

    if (isNaN(x = +x)) return NaN;

    return range[d3.bisect(thresholds, x)];

  }

  scale.domain = function(x) {

    if (!arguments.length) return domain;

    domain = x.filter(function(d) { return !isNaN(d); }).sort(d3.ascending);

    return rescale();

  };

  scale.range = function(x) {

    if (!arguments.length) return range;

    range = x;

    return rescale();

  };

  scale.quantiles = function() {

    return thresholds;

  };

  scale.copy = function() {

    return d3_scale_quantile(domain, range); // copy on write!

  };

  return rescale();

};