Calcs: Fixed calc reducer (#18998)

packages/grafana-data/src/utils/fieldReducer.test.ts

@@ -52,17 +52,13 @@ describe('Stats Calculators', () => {
   it('should calculate basic stats', () => {
     const stats = reduceField({
       field: basicTable.fields[0],
-      reducers: ['first', 'last', 'mean'],
+      reducers: ['first', 'last', 'mean', 'count'],
     });
 
-    // First
     expect(stats.first).toEqual(10);
-
-    // Last
     expect(stats.last).toEqual(20);
-
-    // Mean
     expect(stats.mean).toEqual(15);
+    expect(stats.count).toEqual(2);
   });
 
   it('should support a single stat also', () => {

packages/grafana-data/src/utils/fieldReducer.ts

@@ -247,13 +247,17 @@ function doStandardCalcs(field: Field, ignoreNulls: boolean, nullAsZero: boolean
     // Just used for calcutations -- not exposed as a stat
     previousDeltaUp: true,
   } as FieldCalcs;
+
   const data = field.values;
+  calcs.count = data.length;
 
   for (let i = 0; i < data.length; i++) {
     let currentValue = data.get(i);
+
     if (i === 0) {
       calcs.first = currentValue;
     }
+
     calcs.last = currentValue;
 
     if (currentValue === null) {