Add List#downSample

src/data/List.js

@@ -663,49 +663,53 @@ define(function (require) {
         return result;
     };
 
-    /**
-     * Data mapping to a new List with given dimensions
-     * @param {string|Array.<string>} dimensions
-     * @param {Function} cb
-     * @param {boolean} [stack=false]
-     * @param {*} [context=this]
-     * @return {Array}
-     */
-    listProto.map = function (dimensions, cb, stack, context) {
-        dimensions = zrUtil.map(
-            normalizeDimensions(dimensions), this.getDimension, this
-        );
-
+    function cloneListForMapAndSample(original, excludeDimensions) {
         var allDimensions = this.dimensions;
         var list = new List(
             zrUtil.map(allDimensions, this.getDimensionInfo, this),
             this.hostModel
         );
-
-        // Following properties are all immutable.
-        // So we can reference to the same value
-        var indices = list.indices = this.indices;
-
         // FIXME If needs stackedOn, value may already been stacked
-        transferImmuProperties(list, this, this._wrappedMethods);
+        transferImmuProperties(list, original, original._wrappedMethods);
 
         var storage = list._storage = {};
-        var thisStorage = this._storage;
-
+        var originalStorage = original._storage;
         // Init storage
         for (var i = 0; i < allDimensions.length; i++) {
             var dim = allDimensions[i];
-            var dimStore = thisStorage[dim];
-            if (zrUtil.indexOf(dimensions, dim) >= 0) {
+            var dimStore = originalStorage[dim];
+            if (zrUtil.indexOf(excludeDimensions, dim) >= 0) {
                 storage[dim] = new dimStore.constructor(
-                    thisStorage[dim].length
+                    originalStorage[dim].length
                 );
             }
             else {
-                // Direct copy for other dimensions
-                storage[dim] = thisStorage[dim];
+                // Direct reference for other dimensions
+                storage[dim] = originalStorage[dim];
             }
         }
+        return list;
+    }
+
+    /**
+     * Data mapping to a new List with given dimensions
+     * @param {string|Array.<string>} dimensions
+     * @param {Function} cb
+     * @param {boolean} [stack=false]
+     * @param {*} [context=this]
+     * @return {Array}
+     */
+    listProto.map = function (dimensions, cb, stack, context) {
+        dimensions = zrUtil.map(
+            normalizeDimensions(dimensions), this.getDimension, this
+        );
+
+        var list = cloneListForMapAndSample(this, dimensions);
+        // Following properties are all immutable.
+        // So we can reference to the same value
+        var indices = list.indices = this.indices;
+
+        var storage = list._storage;
 
         var tmpRetValue = [];
         this.each(dimensions, function () {
@@ -731,11 +735,50 @@ define(function (require) {
         return list;
     };
 
-    // Since temporate model is shared by all data items. So we must make sure it can't be write.
-    // PENDING may cause any performance problem?
-    // if (Object.freeze) {
-    //     Object.freeze(temporaryModel);
-    // }
+    /**
+     * Large data down sampling on given dimension
+     * @param {string} dimension
+     * @param {number} rate
+     * @param {Function} sampleValue
+     * @param {Function} sampleIndex Sample index for name and id
+     */
+    listProto.downSample = function (dimension, rate, sampleValue, sampleIndex) {
+        var list = cloneListForMapAndSample(this, [dimension]);
+        var storage = this._storage;
+        var targetStorage = list._storage;
+
+        var originalIndices = this.indices;
+        var indices = list.indices = [];
+
+        var frameValues = [];
+        var frameIndices = [];
+        var frameSize = Math.floor(1 / rate);
+
+        var dimStore = targetStorage[dimension];
+        var len = this.count();
+        // Copy data from original data
+        for (var i = 0; i < storage[dimension].length; i++) {
+            targetStorage[dimension][i] = storage[dimension][i];
+        }
+        for (var i = 0; i < len; i += frameSize) {
+            // Last frame
+            if (frameSize > len - i) {
+                frameSize = len - i;
+                frameValues.length = frameSize;
+            }
+            for (var k = 0; k < frameSize; k++) {
+                frameValues[k] = dimStore[i + k];
+                frameIndices[k] = originalIndices[i + k];
+            }
+            var value = sampleValue(frameValues);
+            var idx = frameIndices[sampleIndex(frameValues, value) || 0];
+            // Only write value on the filtered data
+            dimStore[idx] = value;
+            indices.push(idx);
+        }
+        return list;
+    };
+
     /**
      * Get model of one data item.
      *