Allow records to be removed.

This adds a new method to all crossfilter instances, allowing the
currently-selected records to be removed, e.g.

  var db = crossfilter([1, 2, 3]),
      dimension = db.dimension(Number);
  dimension.filter(1);
  db.remove(); // removes a single record (1), leaving [2, 3]

crossfilter.js

@@ -448,6 +448,7 @@ if (typeof Uint8Array !== "undefined") {
   crossfilter_array32 = function(n) { return new Uint32Array(n); };
 
   crossfilter_arrayLengthen = function(array, length) {
+    if (array.length >= length) return array;
     var copy = new array.constructor(length);
     copy.set(array);
     return copy;
@@ -517,6 +518,7 @@ exports.crossfilter = crossfilter;
 function crossfilter() {
   var crossfilter = {
     add: add,
+    remove: removeData,
     dimension: dimension,
     groupAll: groupAll,
     size: size
@@ -528,7 +530,8 @@ function crossfilter() {
       M = 8, // number of dimensions that can fit in `filters`
       filters = crossfilter_array8(0), // M bits per record; 1 is filtered out
       filterListeners = [], // when the filters change
-      dataListeners = []; // when data is added
+      dataListeners = [], // when data is added
+      removeDataListeners = []; // when data is removed
 
   // Adds the specified new records to this crossfilter.
   function add(newData) {
@@ -548,6 +551,32 @@ function crossfilter() {
     return crossfilter;
   }
 
+  // Removes all records that match the current filters.
+  function removeData() {
+    var newIndex = crossfilter_index(n, n),
+        removed = [];
+    for (var i = 0, j = 0; i < n; ++i) {
+      if (filters[i]) newIndex[i] = j++;
+      else removed.push(i);
+    }
+
+    // Remove all matching records from groups.
+    filterListeners.forEach(function(l) { l(0, [], removed); });
+
+    // Update indexes.
+    removeDataListeners.forEach(function(l) { l(newIndex); });
+
+    // Remove old filters and data by overwriting.
+    for (var i = 0, j = 0, k; i < n; ++i) {
+      if (k = filters[i]) {
+        if (i !== j) filters[j] = k, data[j] = data[i];
+        ++j;
+      }
+    }
+    data.length = j;
+    while (n > j) filters[--n] = 0;
+  }
+
   // Adds a new dimension with the specified value accessor function.
   function dimension(value) {
     var dimension = {
@@ -583,6 +612,8 @@ function crossfilter() {
     dataListeners.unshift(preAdd);
     dataListeners.push(postAdd);
 
+    removeDataListeners.push(removeData);
+
     // Incorporate any existing data into this dimension, and make sure that the
     // filter bitset is wide enough to handle the new dimension.
     m |= one;
@@ -664,6 +695,22 @@ function crossfilter() {
       newValues = newIndex = null;
     }
 
+    function removeData(reIndex) {
+      for (var i = 0, j = 0, k; i < n; ++i) {
+        if (filters[k = index[i]] && i !== j) {
+          values[j] = values[i];
+          index[j] = reIndex[k];
+          ++j;
+        }
+      }
+      values.length = j;
+      while (j < n) index[j++] = 0;
+
+      // Bisect again to recompute lo0 and hi0.
+      var bounds = refilter(values);
+      lo0 = bounds[0], hi0 = bounds[1];
+    }
+
     // Updates the selected values based on the specified bounds [lo, hi].
     // This implementation is used by all the public filter methods.
     function filterIndexBounds(bounds) {
@@ -845,6 +892,7 @@ function crossfilter() {
       // the parent dimension for when data is added, and compute new keys.
       filterListeners.push(update);
       indexListeners.push(add);
+      removeDataListeners.push(removeData);
 
       // Incorporate any existing data into the grouping.
       add(values, index, 0, n);
@@ -958,6 +1006,15 @@ function crossfilter() {
         }
       }
 
+      function removeData() {
+        for (var i = 0, j = 0; i < n; ++i) {
+          if (filters[i]) {
+            if (i !== j) groupIndex[j] = groupIndex[i];
+            ++j;
+          }
+        }
+      }
+
       // Reduces the specified selected or deselected records.
       // This function is only used when the cardinality is greater than 1.
       function updateMany(filterOne, added, removed) {
@@ -1103,6 +1160,8 @@ function crossfilter() {
         if (i >= 0) filterListeners.splice(i, 1);
         i = indexListeners.indexOf(add);
         if (i >= 0) indexListeners.splice(i, 1);
+        i = removeDataListeners.indexOf(removeData);
+        if (i >= 0) removeDataListeners.splice(i, 1);
         return group;
       }
 
@@ -1127,6 +1186,8 @@ function crossfilter() {
       if (i >= 0) dataListeners.splice(i, 1);
       i = dataListeners.indexOf(postAdd);
       if (i >= 0) dataListeners.splice(i, 1);
+      i = removeDataListeners.indexOf(removeData);
+      if (i >= 0) removeDataListeners.splice(i, 1);
       for (i = 0; i < n; ++i) filters[i] &= zero;
       m &= zero;
       return dimension;