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d3_selectionPrototype.data = function(value, key) {
  var i = -1,
      n = this.length,
      group,
      node;

  // If no value is specified, return the first value.
  if (!arguments.length) {
    value = new Array(n = (group = this[0]).length);
    while (++i < n) {
      if (node = group[i]) {
        value[i] = node.__data__;
      }
    }
    return value;
  }

  function bind(group, groupData) {
    var i,
        n = group.length,
        m = groupData.length,
        n0 = Math.min(n, m),
        n1 = Math.max(n, m),
        updateNodes = [],
        enterNodes = [],
        exitNodes = [],
        node,
        nodeData;

    if (key) {
      var nodeByKeyValue = new d3_Map,
          keyValues = [],
          keyValue,
          j = groupData.length;

      for (i = -1; ++i < n;) {
        keyValue = key.call(node = group[i], node.__data__, i);
        if (nodeByKeyValue.has(keyValue)) {
          exitNodes[j++] = node; // duplicate key
        } else {
          nodeByKeyValue.set(keyValue, node);
        }
        keyValues.push(keyValue);
      }

      for (i = -1; ++i < m;) {
        keyValue = key.call(groupData, nodeData = groupData[i], i)
        if (nodeByKeyValue.has(keyValue)) {
          updateNodes[i] = node = nodeByKeyValue.get(keyValue);
          node.__data__ = nodeData;
          enterNodes[i] = exitNodes[i] = null;
        } else {
          enterNodes[i] = d3_selection_dataNode(nodeData);
          updateNodes[i] = exitNodes[i] = null;
        }
        nodeByKeyValue.remove(keyValue);
      }

      for (i = -1; ++i < n;) {
        if (nodeByKeyValue.has(keyValues[i])) {
          exitNodes[i] = group[i];
        }
      }
    } else {
      for (i = -1; ++i < n0;) {
        node = group[i];
        nodeData = groupData[i];
        if (node) {
          node.__data__ = nodeData;
          updateNodes[i] = node;
          enterNodes[i] = exitNodes[i] = null;
        } else {
          enterNodes[i] = d3_selection_dataNode(nodeData);
          updateNodes[i] = exitNodes[i] = null;
        }
      }
      for (; i < m; ++i) {
        enterNodes[i] = d3_selection_dataNode(groupData[i]);
        updateNodes[i] = exitNodes[i] = null;
      }
      for (; i < n1; ++i) {
        exitNodes[i] = group[i];
        enterNodes[i] = updateNodes[i] = null;
      }
    }

    enterNodes.update
        = updateNodes;

    enterNodes.parentNode
        = updateNodes.parentNode
        = exitNodes.parentNode
        = group.parentNode;

    enter.push(enterNodes);
    update.push(updateNodes);
    exit.push(exitNodes);
  }

  var enter = d3_selection_enter([]),
      update = d3_selection([]),
      exit = d3_selection([]);

  if (typeof value === "function") {
    while (++i < n) {
      bind(group = this[i], value.call(group, group.parentNode.__data__, i));
    }
  } else {
    while (++i < n) {
      bind(group = this[i], value);
    }
  }

  update.enter = function() { return enter; };
  update.exit = function() { return exit; };
  return update;
};

function d3_selection_dataNode(data) {
  return {__data__: data};
}
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