fix movingstd (#15911) (#18824)

src/core_plugins/timelion/server/series_functions/__tests__/movingstd.js

@@ -1,24 +1,43 @@
 const filename = require('path').basename(__filename);
 const fn = require(`../${filename}`);
 
-import _ from 'lodash';
+import moment from 'moment';
 const expect = require('chai').expect;
 import invoke from './helpers/invoke_series_fn.js';
+import getSeries from './helpers/get_series';
+import getSeriesList from './helpers/get_series_list';
 
 describe(filename, () => {
 
-  let seriesList;
-  beforeEach(() => {
-    seriesList = require('./fixtures/seriesList.js')();
-  });
+  it('computes the moving standard deviation of a list', async () => {
+    const points = [
+      108.48, 111.56, 112.13, 113.75, 114.25, 110.79, 111.21, 116.82, 117.16, 120.38, 116.96,
+      119.56, 118.97, 117.54, 114.42, 111.01, 114.20, 116.43, 117.74, 119.90, 124.65, 124.98,
+      124.70, 123.60, 124.5, 126.85];
+    const buckets = [];
+    buckets[0] = moment('2018-01-01T00:00:00.000Z');
+    for (let i = 1; i < points.length; i++) {
+      buckets[i] = buckets[i - 1].add(1, 'hours');
+    }
+    const series = getSeries('test data', buckets, points);
+    const seriesList = getSeriesList([series]);
+    const numWindows = 5;
+    const position = 'left';
+    const results = await invoke(fn, [seriesList, numWindows, position]);
 
-  it('computes the moving standard deviation of a list', () => {
-    return invoke(fn, [seriesList, 2]).then((r) => {
-      const values = _.map(r.output.list[1].data, 1);
-      expect(values[0]).to.equal(null);
-      expect(values[1]).to.equal(null);
-      expect(values[2]).to.be.within(26, 27);
-      expect(values[3]).to.be.within(7, 8);
+    const resultPoints = results.output.list[0].data.map((row) => {
+      // row is an array; index 0 is the time bucket, index 1 is the value
+      return row[1];
+    });
+    // First 5 result buckets are null since moving window is filling up.
+    const trimmedResultPoints = resultPoints.slice(numWindows);
+
+    const expectedPoints = [
+      2.28, 1.46, 1.53, 2.46, 3.00, 4.14, 3.31, 1.67, 1.50, 1.41,
+      2.01, 3.56, 3.12, 2.50, 2.56, 3.41, 3.97, 3.92, 3.35, 2.12, 0.52];
+
+    expectedPoints.forEach((value, index) => {
+      expect(trimmedResultPoints[index]).to.be.within(value - 0.01, value + 0.01);
     });
   });
 

src/core_plugins/timelion/server/series_functions/movingstd.js

@@ -2,6 +2,9 @@ import alter from '../lib/alter.js';
 import _ from 'lodash';
 import Chainable from '../lib/classes/chainable';
 
+const positions = ['left', 'right', 'center'];
+const defaultPosition = positions[0];
+
 export default new Chainable('movingstd', {
   args: [
     {
@@ -11,36 +14,61 @@ export default new Chainable('movingstd', {
     {
       name: 'window',
       types: ['number'],
-      help: 'Number of points to compute the standard deviation over'
+      help: 'Number of points to compute the standard deviation over.'
+    },
+    {
+      name: 'position',
+      types: ['string', 'null'],
+      help: `Position of the window slice relative to the result time. Options are ${positions.join(', ')}. Default: ${defaultPosition}`
     }
   ],
   aliases: ['mvstd'],
   help: 'Calculate the moving standard deviation over a given window. Uses naive two-pass algorithm. Rounding errors ' +
     'may become more noticeable with very long series, or series with very large numbers.',
   fn: function movingstdFn(args) {
-    return alter(args, function (eachSeries, _window) {
+    return alter(args, function (eachSeries, _window, _position) {
+
+      _position = _position || defaultPosition;
+
+      if (!_.contains(positions, _position)) throw new Error('Valid positions are: ' + positions.join(', '));
 
       const pairs = eachSeries.data;
+      const pairsLen = pairs.length;
+      eachSeries.label = eachSeries.label + ' mvstd=' + _window;
 
-      eachSeries.data = _.map(pairs, function (point, i) {
-        if (i < _window) { return [point[0], null]; }
+      function toPoint(point, pairSlice) {
+        const average = _.chain(pairSlice).map(1).reduce(function (memo, num) {
+          return memo + num;
+        }).value() / _window;
 
-        const average = _.chain(pairs.slice(i - _window, i))
-          .map(function (point) {
-            return point[1];
-          }).reduce(function (memo, num) {
-            return (memo + num);
-          }).value() / _window;
-
-        const variance = _.chain(pairs.slice(i - _window, i))
-          .map(function (point) {
-            return point[1];
-          }).reduce(function (memo, num) {
-            return memo + Math.pow(num - average, 2);
-          }).value() / (_window - 1);
+        const variance = _.chain(pairSlice).map(function (point) {
+          return Math.pow(point[1] - average, 2);
+        }).reduce(function (memo, num) {
+          return memo + num;
+        }).value() / (_window - 1);
 
         return [point[0], Math.sqrt(variance)];
-      });
+      }
+
+      if (_position === 'center') {
+        const windowLeft = Math.floor(_window / 2);
+        const windowRight = _window - windowLeft;
+        eachSeries.data = _.map(pairs, function (point, i) {
+          if (i < windowLeft || i >= pairsLen - windowRight) return [point[0], null];
+          return toPoint(point, pairs.slice(i - windowLeft, i + windowRight));
+        });
+      } else if (_position === 'left') {
+        eachSeries.data = _.map(pairs, function (point, i) {
+          if (i < _window) return [point[0], null];
+          return toPoint(point, pairs.slice(i - _window, i));
+        });
+      } else if (_position === 'right') {
+        eachSeries.data = _.map(pairs, function (point, i) {
+          if (i >= pairsLen - _window) return [point[0], null];
+          return toPoint(point, pairs.slice(i, i + _window));
+        });
+      }
+
       return eachSeries;
     });
   }