Function map

explainshell/web/static/js/d3.v3.js:254–277

(mapType, array, depth)

  d3.nest = function() {
    var nest = {}, keys = [], sortKeys = [], sortValues, rollup;
    function map(mapType, array, depth) {
      if (depth >= keys.length) return rollup ? rollup.call(nest, array) : sortValues ? array.sort(sortValues) : array;
      var i = -1, n = array.length, key = keys[depth++], keyValue, object, setter, valuesByKey = new d3_Map(), values;
      while (++i < n) {
        if (values = valuesByKey.get(keyValue = key(object = array[i]))) {
          values.push(object);
        } else {
          valuesByKey.set(keyValue, [ object ]);
        }
      }
      if (mapType) {
        object = mapType();
        setter = function(keyValue, values) {
          object.set(keyValue, map(mapType, values, depth));
        };
      } else {
        object = {};
        setter = function(keyValue, values) {
          object[keyValue] = map(mapType, values, depth);
        };
      }
      valuesByKey.forEach(setter);
      return object;
    }
    function entries(map, depth) {
      if (depth >= keys.length) return map;
      var array = [], sortKey = sortKeys[depth++];