[ML] Extend population preview chart to show actual and typical value (#67569)

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugins/ml/public/application/explorer/explorer_charts/explorer_chart_distribution.js

@@ -25,6 +25,7 @@ import {
   getTickValues,
   numTicksForDateFormat,
   removeLabelOverlap,
+  chartExtendedLimits,
 } from '../../util/chart_utils';
 import { LoadingIndicator } from '../../components/loading_indicator/loading_indicator';
 import { getTimeBucketsFromCache } from '../../util/time_buckets';
@@ -98,7 +99,7 @@ export class ExplorerChartDistribution extends React.Component {
     const filteredChartData = init(config);
     drawRareChart(filteredChartData);
 
-    function init({ chartData }) {
+    function init({ chartData, functionDescription }) {
       const $el = $('.ml-explorer-chart');
 
       // Clear any existing elements from the visualization,
@@ -137,22 +138,24 @@ export class ExplorerChartDistribution extends React.Component {
       });
 
       if (chartType === CHART_TYPE.POPULATION_DISTRIBUTION) {
-        const focusData = chartData
-          .filter((d) => {
-            return d.entity === highlight;
-          })
-          .map((d) => d.value);
-        const focusExtent = d3.extent(focusData);
-
+        const focusData = chartData.filter((d) => {
+          return d.entity === highlight;
+        });
+        // calculate the max y domain based on value, typical, and actual
+        // also sets the min to be at least 0 if the series function type is `count`
+        const { min: yScaleDomainMin, max: yScaleDomainMax } = chartExtendedLimits(
+          focusData,
+          functionDescription
+        );
         // now again filter chartData to include only the data points within the domain
         chartData = chartData.filter((d) => {
-          return d.value <= focusExtent[1];
+          return d.value <= yScaleDomainMax;
         });
 
         lineChartYScale = d3.scale
           .linear()
           .range([chartHeight, 0])
-          .domain([0, focusExtent[1]])
+          .domain([yScaleDomainMin < 0 ? yScaleDomainMin : 0, yScaleDomainMax])
           .nice();
       } else if (chartType === CHART_TYPE.EVENT_DISTRIBUTION) {
         // avoid overflowing the border of the highlighted area

x-pack/plugins/ml/public/application/util/chart_utils.js

@@ -65,6 +65,44 @@ export function chartLimits(data = []) {
   return limits;
 }
 
+export function chartExtendedLimits(data = [], functionDescription) {
+  let _min = Infinity;
+  let _max = -Infinity;
+  data.forEach((d) => {
+    let metricValue = d.value;
+    const actualValue = Array.isArray(d.actual) ? d.actual[0] : d.actual;
+    const typicalValue = Array.isArray(d.typical) ? d.typical[0] : d.typical;
+
+    if (metricValue === null && d.anomalyScore !== undefined && d.actual !== undefined) {
+      // If an anomaly coincides with a gap in the data, use the anomaly actual value.
+      metricValue = actualValue;
+    }
+
+    if (d.anomalyScore !== undefined) {
+      _min = Math.min(_min, metricValue, actualValue, typicalValue);
+      _max = Math.max(_max, metricValue, actualValue, typicalValue);
+    } else {
+      _min = Math.min(_min, metricValue);
+      _max = Math.max(_max, metricValue);
+    }
+  });
+  const limits = { max: _max, min: _min };
+
+  // add padding of 5% of the difference between max and min
+  // if we ended up with the same value for both of them
+  if (limits.max === limits.min) {
+    const padding = limits.max * 0.05;
+    limits.max += padding;
+    limits.min -= padding;
+  }
+
+  // makes sure the domain starts at 0 if the aggregation is by count
+  // since the number should always be positive
+  if (functionDescription === 'count' && limits.min < 0) {
+    limits.min = 0;
+  }
+  return limits;
+}
 export function drawLineChartDots(data, lineChartGroup, lineChartValuesLine, radius = 1.5) {
   // We need to do this because when creating a line for a chart which has data gaps,
   // if there are single datapoints without any valid data before and after them,