Histogram: filter nulls, bucket-adaptive xAxis decimals (#51773)

packages/grafana-data/src/transformations/transformers/histogram.ts

@@ -160,13 +160,13 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
     for (const frame of frames) {
       for (const field of frame.fields) {
         if (field.type === FieldType.number) {
-          allValues = allValues.concat(
-            field.values.toArray().map((val: number) => Number(val.toFixed(field.config.decimals ?? 0)))
-          );
+          allValues = allValues.concat(field.values.toArray());
         }
       }
     }
 
+    allValues = allValues.filter((v) => v != null);
+
     allValues.sort((a, b) => a - b);
 
     let smallestDelta = Infinity;
@@ -204,6 +204,9 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
 
   const getBucket = (v: number) => incrRoundDn(v - bucketOffset, bucketSize!) + bucketOffset;
 
+  // guess number of decimals
+  let bucketDecimals = (('' + bucketSize).match(/\.\d+$/) ?? ['.'])[0].length - 1;
+
   let histograms: AlignedData[] = [];
   let counts: Field[] = [];
   let config: FieldConfig | undefined = undefined;
@@ -220,7 +223,7 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
             unit: undefined,
           },
         });
-        if (!config && Object.keys(field.config).length) {
+        if (!config && field.config.unit) {
           config = field.config;
         }
       }
@@ -251,7 +254,13 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
     values: new ArrayVector(joinedHists[0]),
     type: FieldType.number,
     state: undefined,
-    config: config ?? {},
+    config:
+      bucketDecimals === 0
+        ? config ?? {}
+        : {
+            ...config,
+            decimals: bucketDecimals,
+          },
   };
   const bucketMax = {
     ...bucketMin,