Aggregate dataset by ticks

aggregate.js

/**
 * Aggregates a dataset containing {x,y} values by an array of x-axis ticks
 * where the aggregated dataset contains one {x,y} value per specified
 * tick.
 * @param dataset input dataset of {x,y} values
 * @param ticks array of ticks to aggregate by
 * @return new dataset containing aggregated {x,y} values
 */
function aggregate(dataset, ticks) {
  return _.chain(dataset)
    .filter(function(data) {
      return (data.x >= ticks[0] && data.x < ticks[ticks.length - 1]);
    })
    .groupBy(function(data) {
      for (var i = 0; i < ticks.length; i++) {
        if (data.x < ticks[i]) {
          return i - 1;
        }
      }
      return ticks.length - 1;
    })
    .map(function(group, i) {
      return _.reduce(group, function(memo, data) {
        memo.y += data.y;
        return memo;
      }, { x: ticks[i], y: 0 });
    }).value();
}