Add transformScatterData utility method

Transforms the raw scatter data into
a two-dimensional array

ee/app/assets/javascripts/analytics/productivity_analytics/utils.js

@@ -44,6 +44,49 @@ export const initDateArray = (startDate, endDate) => {
   return Array.from({ length: days + 1 }, () => []);
 };
 
+/**
+ * Transforms the raw scatter data into a data strucuture that allows easy access.
+ * It creates a two dimensional array where each item in the first dimension corresponds to one day (date).
+ *
+ * I.e., the first item corresponds to the start date, the second item corresponds to the start date plus one day,
+ * the last item corresponds to the end date.
+ *
+ * For each date, we store an array of individual MRs for the particular date (i.e, the second dimension) in the following form:
+ * { merged_at: '2019-09-01T04:55:05.757Z', metric: 10 }
+ *
+ * Given that startDate=2019-09-01 and endDate=2019-09-03 we receive the following data structure:
+ * [
+ *   [{ merged_at: '2019-09-01T04:55:05.757Z', metric: 10 }, { merged_at: '2019-09-01T14:12:09.757Z', metric: 8 }, { ... }] // 2019-09-01
+ *   [{ merged_at: '2019-09-02T08:29:33.748Z', metric: 7 }, ... ] // 2019-09-02
+ *   [{ merged_at: '2019-09-03T21:29:49.351Z', metric: 24 }, ... ] // 2019-09-03
+ * ]
+ *
+ * @param {*} data - The raw data received from the API.
+ * @param {*} startDate - The start date selected by the user minus an additional offset in days (e.g., 30 days).
+ * @param {*} endDate - The end date selected by the user.
+ * @returns {Array} The transformed data array (first item corresponds to start date, last item to end date)
+ */
+export const transformScatterData = (data, startDate, endDate) => {
+  const result = initDateArray(startDate, endDate);
+  const totalItems = result.length;
+
+  Object.keys(data).forEach(id => {
+    const mergedAtDate = new Date(data[id].merged_at);
+    const d = new Date();
+    d.setDate(mergedAtDate.getDate());
+    d.setMonth(mergedAtDate.getMonth());
+    d.setFullYear(mergedAtDate.getFullYear());
+
+    const dayDiff = getDayDifference(d, endDate);
+    if (dayDiff > -1) {
+      const idx = totalItems - (dayDiff + 1);
+      result[idx].push(data[id]);
+    }
+  });
+
+  return result;
+};
+
 /**
  * Transforms a given data object into an array
  * which will be used as series data for the scatterplot chart.

ee/spec/frontend/analytics/productivity_analytics/utils_spec.js

@@ -2,6 +2,7 @@ import {
   getLabelsEndpoint,
   getMilestonesEndpoint,
   initDateArray,
+  transformScatterData,
   getScatterPlotData,
   getMedianLineData,
 } from 'ee/analytics/productivity_analytics/utils';
@@ -45,6 +46,29 @@ describe('Productivity Analytics utils', () => {
     });
   });
 
+  describe('transformScatterData', () => {
+    it('transforms the raw scatter data into a two-dimensional array and groups by date', () => {
+      const startDate = new Date('2019-08-01');
+      const endDate = new Date('2019-08-03');
+      const data = {
+        1: { merged_at: '2019-08-01T11:10:00.000Z', metric: 10 },
+        2: { merged_at: '2019-08-01T12:11:00.000Z', metric: 20 },
+        3: { merged_at: '2019-08-02T13:13:00.000Z', metric: 30 },
+        4: { merged_at: '2019-08-03T14:14:00.000Z', metric: 40 },
+      };
+      const result = transformScatterData(data, startDate, endDate);
+      const expected = [
+        [
+          { merged_at: '2019-08-01T11:10:00.000Z', metric: 10 },
+          { merged_at: '2019-08-01T12:11:00.000Z', metric: 20 },
+        ],
+        [{ merged_at: '2019-08-02T13:13:00.000Z', metric: 30 }],
+        [{ merged_at: '2019-08-03T14:14:00.000Z', metric: 40 }],
+      ];
+      expect(result).toEqual(expected);
+    });
+  });
+
   describe('getScatterPlotData', () => {
     it('filters out data before given "dateInPast", transforms the data and sorts by date ascending', () => {
       const dateInPast = new Date(2019, 7, 9); // '2019-08-09T22:00:00.000Z';