feat(transform): add exponential smoothing data transform methods

__tests__/plots/static/ema-basic.ts

@@ -0,0 +1,37 @@
+import { G2Spec } from '../../../src';
+
+export function emaBasic(): G2Spec {
+  return {
+    type: 'view',
+    children: [
+      {
+        type: 'line',
+        data: {
+          type: 'fetch',
+          value: 'data/aapl.csv',
+          transform: [
+            {
+              type: 'ema',
+              field: 'close',
+              alpha: 0.8,
+            },
+          ],
+        },
+      },
+      {
+        type: 'line',
+        style: {
+          opacity: 0.3,
+        },
+        data: {
+          type: 'fetch',
+          value: 'data/aapl.csv',
+        },
+      },
+    ],
+    encode: {
+      x: 'date',
+      y: 'close',
+    },
+  };
+}

__tests__/plots/static/index.ts

@@ -62,6 +62,7 @@ export { aaplLineAreaBasicSample } from './aapl-line-area-basic-sample';
 export { aaplAreaLineSmoothSample } from './aapl-area-line-smooth-sample';
 export { aaplLinePointBasicSample } from './aapl-line-point-basic-sample';
 export { speciesDensityBasic } from './species-density-basic';
+export { emaBasic } from './ema-basic';
 export { speciesViolinBasic } from './species-violin-basic';
 export { speciesViolinBasicPolar } from './species-violin-basic-polar';
 export { unemploymentLineMultiSeries } from './unemployment-line-multi-series';

__tests__/unit/data/ema.spec.ts

@@ -0,0 +1,101 @@
+import { EMA } from '../../../src/data';
+
+describe('EMA', () => {
+  it('EMA({...}) returns a function  that is used to exponentially smooth the data', async () => {
+    const transform = EMA({ alpha: 0.6, field: 'y' });
+    const data = [
+      { x: 1, y: 2 },
+      { x: 4, y: 5 },
+      { x: 5, y: 8 },
+    ];
+    const r = await transform(data);
+    r.forEach((d, i) => {
+      if (i > 0) {
+        expect(d.y).not.toBe(data[i].y);
+      } else {
+        expect(d.y).toBe(data[i].y);
+      }
+      expect(d.x).toBe(data[i].x);
+    });
+  });
+
+  it('The "field" field determines the smoothed data', () => {
+    const transform = EMA({ alpha: 0.6, field: 'x' });
+    const data = [
+      { x: 1, y: 2 },
+      { x: 4, y: 5 },
+      { x: 5, y: 8 },
+    ];
+    const r = transform(data);
+    r.forEach((d, i) => {
+      if (i > 0) {
+        expect(d.x).not.toBe(data[i].x);
+      } else {
+        expect(d.x).toBe(data[i].x);
+      }
+      expect(d.y).toBe(data[i].y);
+    });
+  });
+
+  it('The as field will avoid overwriting the original data', () => {
+    const transform = EMA({ alpha: 0.6, field: 'y', as: 'smooth' });
+    const data = [
+      { x: 1, y: 2 },
+      { x: 4, y: 5 },
+      { x: 5, y: 8 },
+    ];
+    const r = transform(data);
+    expect(r).toEqual([
+      {
+        x: 1,
+        y: 2,
+        smooth: 2,
+      },
+      {
+        x: 4,
+        y: 5,
+        smooth: 3.2,
+      },
+      {
+        x: 5,
+        y: 8,
+        smooth: 5.12,
+      },
+    ]);
+  });
+
+  it('should handle missing field values', function () {
+    const data = [{ x: 1 }, { y: 2 }, { y: 3 }, { x: 4 }];
+    const result = EMA({ field: 'y' })(data);
+    expect(result[0].y).toBe(undefined);
+    expect(result[1].y).not.toBe(undefined);
+    expect(result[2].y).not.toBe(undefined);
+    expect(result[3].y).toBe(undefined);
+  });
+
+  it('should handle missing alpha value', function () {
+    const data = [{ y: 1 }, { y: 2 }, { y: 3 }];
+    const r = EMA({ field: 'y' })(data);
+    r.forEach((d, i) => {
+      if (i > 0) {
+        expect(d.y).not.toBe(data[i].y);
+      } else {
+        expect(d.y).toBe(data[i].y);
+      }
+    });
+  });
+  it('The value of alpha should be greater than zero and less than one', function () {
+    const data = [{ y: 1 }, { y: 2 }, { y: 3 }];
+    let alpha = 1.1;
+    expect(() => EMA({ field: 'y', alpha })(data)).toThrowError();
+
+    alpha = -0.1;
+    expect(() => EMA({ field: 'y', alpha })(data)).toThrowError();
+  });
+
+  it('Returns an empty array if entered', function () {
+    const data = [];
+    const result = EMA({ field: 'y' })(data);
+    expect(result).toEqual([]);
+  });
+});

__tests__/unit/lib/core.spec.ts

@@ -156,6 +156,7 @@ import {
   KDE,
   Log as DataLog,
   WordCloud,
+  EMA,
 } from '../../../src/data';
 import {
   OverflowHide,
@@ -182,6 +183,7 @@ describe('corelib', () => {
       'data.join': Join,
       'data.kde': KDE,
       'data.log': DataLog,
+      'data.ema': EMA,
       'data.wordCloud': WordCloud,
       'transform.stackY': StackY,
       'transform.binX': BinX,

__tests__/unit/lib/std.spec.ts

@@ -170,6 +170,7 @@ import {
   Arc,
   Log as DataLog,
   WordCloud,
+  EMA,
 } from '../../../src/data';
 import {
   OverflowHide,
@@ -196,6 +197,7 @@ describe('stdlib', () => {
       'data.join': Join,
       'data.kde': KDE,
       'data.venn': Venn,
+      'data.ema': EMA,
       'data.wordCloud': WordCloud,
       'data.cluster': Cluster,
       'data.arc': Arc,

site/docs/spec/data/ema.en.md

@@ -0,0 +1,6 @@
+---
+title: ema
+order: 1
+---
+
+<embed src="@/docs/spec/data/ema.zh.md"></embed>

site/docs/spec/data/ema.zh.md

@@ -0,0 +1,116 @@
+---
+title: ema
+order: 1
+---
+
+
+EMA（Exponential Moving Average）是一种常用的平滑算法，用于计算数据的指数移动平均值。它通过给较近的数据赋予权重来平滑数据，从而减少噪声和波动。
+
+在模型训练中，可以使用EMA来平滑数据，观察数据变化趋势。
+
+如下公式显示，α越大平滑效果更明显
+
+
+$EMA_t =  (1 - \alpha) \cdot P_t +  \alpha \cdot EMA_{t-1}$
+
+具体细节可参考[文档](https://en.wikipedia.org/wiki/Exponential_smoothing)  
+
+
+
+## 开始使用
+
+```ts
+const data = [
+  { x: 1, y: 2 },
+  { x: 4, y: 5 },
+  { x: 5, y: 8 },
+];
+
+chart
+  .data({
+    type: 'line',
+    value: data,
+    transform: [
+      {
+        type: 'ema',
+        field: 'y',
+        alpha: 0.6,
+        as: 'other'
+      },
+    ],
+  });
+```
+
+上述例子处理之后，数据变成为：
+
+```js
+[
+  {
+    "x": 1,
+    "y": 2,
+    "other": 2,
+  },
+  {
+    "x": 4,
+    "y": 3.2,
+    "other": 3.2,
+  },
+  {
+    "x": 5,
+    "y": 5.12,
+    "other": 5.12,
+  }
+];
+```
+
+## 开始使用
+
+```js | ob
+(() => {
+  const chart = new G2.Chart();
+
+  chart.options({
+    type: 'view',
+    children: [
+      {
+        type: 'line',
+        data: {
+          type: 'fetch',
+          value: 'https://gw.alipayobjects.com/os/bmw-prod/551d80c6-a6be-4f3c-a82a-abd739e12977.csv',
+          transform: [
+            {
+              type: 'ema',
+              field: 'close',
+              alpha: 0.8,
+            },
+          ],
+        },
+      },
+      {
+        type: 'line',
+        style: {
+          opacity: 0.3,
+        },
+        data: {
+          type: 'fetch',
+          value: 'https://gw.alipayobjects.com/os/bmw-prod/551d80c6-a6be-4f3c-a82a-abd739e12977.csv',
+        },
+      },
+    ],
+    encode: {
+      x: 'date',
+      y: 'close',
+    },
+  });
+
+  return chart.render().then((chart) => chart.getContainer());
+})();
+```
+
+## 选项
+
+| 属性 | 描述 | 类型 | 默认值|
+| -------------| ----------------------------------------------------------- | -----------------------------| --------------------|
+| field     |  需要处理的字段列表                             | string    |  y          |
+| alpha     |  平滑因子,范围在0-1                             | number   | 0.6          |
+| as     |         存储的字段, 默认是field传入的值，可自定义字段避免覆盖原字段数据                     | string   | y          |

src/data/ema.ts

@@ -0,0 +1,62 @@
+import { DataComponent as DC } from '../runtime';
+import { EMADataTransform } from '../spec';
+
+export function ema(values: number[], alpha: number): number[] {
+  if (alpha < 0 || alpha > 1) {
+    throw new Error('alpha must be between 0 and 1.');
+  }
+  if (values.length === 0) {
+    return [];
+  }
+
+  let last = values[0];
+  const smoothed: number[] = [];
+
+  for (const point of values) {
+    if (point === null || point === undefined) {
+      // 如果没有数据的话，使用最近的值
+      smoothed.push(point);
+      console.warn('EMA：The value is null or undefined', values);
+      continue;
+    }
+
+    if (last === null || last === undefined) {
+      last = point;
+    }
+
+    const smoothedVal = last * alpha + (1 - alpha) * point;
+    smoothed.push(smoothedVal);
+    last = smoothedVal;
+  }
+
+  return smoothed;
+}
+
+export type EMAOptions = Omit<EMADataTransform, 'type'>;
+
+/**
+ * https://en.wikipedia.org/wiki/Exponential_smoothing
+ * @param options
+ * @returns
+ */
+
+export const EMA: DC<EMAOptions> = (options) => {
+  const { field = 'y', alpha = 0.6, as = field } = options;
+
+  return (data) => {
+    const values = data.map((d) => {
+      return d[field];
+    });
+
+    const out = ema(values, alpha);
+
+    return data.map((d, i) => {
+      return {
+        ...d,
+        [as]: out[i],
+      };
+    });
+  };
+};
+
+EMA.props = {};

src/data/index.ts

@@ -18,6 +18,7 @@ export { Slice } from './slice';
 export { KDE } from './kde';
 export { Venn } from './venn';
 export { Log } from './log';
+export { EMA } from './ema';
 
 export type { FetchOptions } from './fetch';
 export type { FoldOptions } from './fold';
@@ -39,3 +40,4 @@ export type { SliceOptions } from './slice';
 export type { KDEOptions } from './kde';
 export type { VennOptions } from './venn';
 export type { LogDataOptions } from './log';
+export type { EMAOptions } from './ema';

src/lib/core.ts

@@ -154,6 +154,7 @@ import {
   Sort as DataSort,
   KDE as DataKDE,
   Log as DataLog,
+  EMA as DataEMA,
   WordCloud,
 } from '../data';
 import {
@@ -181,6 +182,7 @@ export function corelib() {
     'data.kde': DataKDE,
     'data.log': DataLog,
     'data.wordCloud': WordCloud,
+    'data.ema': DataEMA,
     'transform.stackY': StackY,
     'transform.binX': BinX,
     'transform.bin': Bin,