--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/javascript/d3/src/core/nest.js	Thu Apr 10 14:20:23 2014 +0200
@@ -0,0 +1,87 @@
+d3.nest = function() {
+  var nest = {},
+      keys = [],
+      sortKeys = [],
+      sortValues,
+      rollup;
+
+  function map(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,
+        o = {};
+
+    while (++i < n) {
+      if ((keyValue = key(object = array[i])) in o) {
+        o[keyValue].push(object);
+      } else {
+        o[keyValue] = [object];
+      }
+    }
+
+    for (keyValue in o) {
+      o[keyValue] = map(o[keyValue], depth);
+    }
+
+    return o;
+  }
+
+  function entries(map, depth) {
+    if (depth >= keys.length) return map;
+
+    var a = [],
+        sortKey = sortKeys[depth++],
+        key;
+
+    for (key in map) {
+      a.push({key: key, values: entries(map[key], depth)});
+    }
+
+    if (sortKey) a.sort(function(a, b) {
+      return sortKey(a.key, b.key);
+    });
+
+    return a;
+  }
+
+  nest.map = function(array) {
+    return map(array, 0);
+  };
+
+  nest.entries = function(array) {
+    return entries(map(array, 0), 0);
+  };
+
+  nest.key = function(d) {
+    keys.push(d);
+    return nest;
+  };
+
+  // Specifies the order for the most-recently specified key.
+  // Note: only applies to entries. Map keys are unordered!
+  nest.sortKeys = function(order) {
+    sortKeys[keys.length - 1] = order;
+    return nest;
+  };
+
+  // Specifies the order for leaf values.
+  // Applies to both maps and entries array.
+  nest.sortValues = function(order) {
+    sortValues = order;
+    return nest;
+  };
+
+  nest.rollup = function(f) {
+    rollup = f;
+    return nest;
+  };
+
+  return nest;
+};