fix(sample): fix minmax sampling behaviour

src/data/DataStore.ts

@@ -1013,6 +1013,75 @@ class DataStore {
         return target;
     }
 
+    /**
+     * Large data down sampling using min-max
+     * @param {string} valueDimension
+     * @param {number} rate
+     */
+    minmaxDownSample(
+        valueDimension: DimensionIndex,
+        rate: number
+    ): DataStore {
+        const target = this.clone([valueDimension], true);
+        const targetStorage = target._chunks;
+
+        const frameSize = Math.floor(1 / rate);
+
+        const dimStore = targetStorage[valueDimension];
+        const len = this.count();
+
+        // Each frame results in 2 data points, one for min and one for max
+        const newIndices = new (getIndicesCtor(this._rawCount))(Math.ceil(len / frameSize) * 2);
+
+        let offset = 0;
+        for (let i = 0; i < len; i += frameSize) {
+            let minIndex = i;
+            let minValue = dimStore[this.getRawIndex(minIndex)];
+            let maxIndex = i;
+            let maxValue = dimStore[this.getRawIndex(maxIndex)];
+
+            let thisFrameSize = frameSize;
+            // Handle final smaller frame
+            if (i + frameSize > len) {
+                thisFrameSize = len - i;
+            }
+            // Determine min and max within the current frame
+            for (let k = 0; k < thisFrameSize; k++) {
+                const rawIndex = this.getRawIndex(i + k);
+                const value = dimStore[rawIndex];
+
+                if (value < minValue) {
+                    minValue = value;
+                    minIndex = i + k;
+                }
+                if (value > maxValue) {
+                    maxValue = value;
+                    maxIndex = i + k;
+                }
+            }
+
+            const rawMinIndex = this.getRawIndex(minIndex);
+            const rawMaxIndex = this.getRawIndex(maxIndex);
+
+            // Set the order of the min and max values, based on their ordering in the frame
+            if (minIndex < maxIndex) {
+                newIndices[offset++] = rawMinIndex;
+                newIndices[offset++] = rawMaxIndex;
+            }
+            else {
+                newIndices[offset++] = rawMaxIndex;
+                newIndices[offset++] = rawMinIndex;
+            }
+        }
+
+        target._count = offset;
+        target._indices = newIndices;
+
+        target._updateGetRawIdx();
+
+        return target;
+    }
+
 
     /**
      * Large data down sampling on given dimension

src/data/SeriesData.ts

@@ -254,10 +254,10 @@ class SeriesData<
 
     // Methods that create a new list based on this list should be listed here.
     // Notice that those method should `RETURN` the new list.
-    TRANSFERABLE_METHODS = ['cloneShallow', 'downSample', 'lttbDownSample', 'map'] as const;
+    TRANSFERABLE_METHODS = ['cloneShallow', 'downSample', 'minmaxDownSample', 'lttbDownSample', 'map'] as const;
     // Methods that change indices of this list should be listed here.
     CHANGABLE_METHODS = ['filterSelf', 'selectRange'] as const;
-    DOWNSAMPLE_METHODS = ['downSample', 'lttbDownSample'] as const;
+    DOWNSAMPLE_METHODS = ['downSample', 'minmaxDownSample', 'lttbDownSample'] as const;
 
     /**
      * @param dimensionsInput.dimensions
@@ -1098,6 +1098,23 @@ class SeriesData<
         return list as SeriesData<HostModel>;
     }
 
+    /**
+     * Large data down sampling using min-max
+     * @param {string} valueDimension
+     * @param {number} rate
+     */
+    minmaxDownSample(
+        valueDimension: DimensionLoose,
+        rate: number
+    ): SeriesData<HostModel> {
+        const list = cloneListForMapAndSample(this);
+        list._store = this._store.minmaxDownSample(
+            this._getStoreDimIndex(valueDimension),
+            rate
+        );
+        return list as SeriesData<HostModel>;
+    }
+
     /**
      * Large data down sampling using largest-triangle-three-buckets
      * @param {string} valueDimension

src/processor/dataSample.ts

@@ -61,22 +61,6 @@ const samplers: Dictionary<Sampler> = {
         // NaN will cause illegal axis extent.
         return isFinite(min) ? min : NaN;
     },
-    minmax: function (frame) {
-        let turningPointAbsoluteValue = -Infinity;
-        let turningPointOriginalValue = -Infinity;
-
-        for (let i = 0; i < frame.length; i++) {
-            const originalValue = frame[i];
-            const absoluteValue = Math.abs(originalValue);
-
-            if (absoluteValue > turningPointAbsoluteValue) {
-                turningPointAbsoluteValue = absoluteValue;
-                turningPointOriginalValue = originalValue;
-            }
-        }
-
-        return isFinite(turningPointOriginalValue) ? turningPointOriginalValue : NaN;
-    },
     // TODO
     // Median
     nearest: function (frame) {
@@ -115,6 +99,9 @@ export default function dataSample(seriesType: string): StageHandler {
                     if (sampling === 'lttb') {
                         seriesModel.setData(data.lttbDownSample(data.mapDimension(valueAxis.dim), 1 / rate));
                     }
+                    else if (sampling === 'minmax') {
+                        seriesModel.setData(data.minmaxDownSample(data.mapDimension(valueAxis.dim), 1 / rate));
+                    }
                     let sampler;
                     if (isString(sampling)) {
                         sampler = samplers[sampling];