Remove Continuous vars with 1 value from histogram, add to info drawer (#1927)

* remove single val continous metadata from histogram, add to info drawer

* refactor to save singleContinuous values in state

* fix edge case, single continuous values reappeard in rsb when clipped

client/src/components/brushableHistogram/index.js

@@ -450,6 +450,7 @@ const Histogram = ({
     isScatterplotYYaccessor: state.controls.scatterplotYYaccessor === field,
     continuousSelectionRange: state.continuousSelection[myName],
     isColorAccessor: state.colors.colorAccessor === field,
+    singleContinuousValues: state.singleContinuousValue.singleContinuousValues,
   };
 })
 class HistogramBrush extends React.PureComponent {
@@ -608,18 +609,44 @@ class HistogramBrush extends React.PureComponent {
   };
 
   fetchAsyncProps = async () => {
-    const { annoMatrix } = this.props;
+    const { annoMatrix, field, dispatch, singleContinuousValues } = this.props;
     const { isClipped } = annoMatrix;
-
+    if (singleContinuousValues.has(field)) {
+      return {
+        histogram: undefined,
+        range: undefined,
+        unclippedRange: undefined,
+        unclippedRangeColor: globals.blue,
+        isSingleValue: true,
+        OK2Render: false,
+      };
+    }
     const query = this.createQuery();
     const df = await annoMatrix.fetch(...query);
     const column = df.icol(0);
 
-    // if we are clipped, fetch both our value and our unclipped value,
-    // as we need the absolute min/max range, not just the clipped min/max.
     const summary = column.summarize();
     const range = [summary.min, summary.max];
 
+    if (summary.min === summary.max && !isClipped) {
+      dispatch({
+        type: "add single continuous value",
+        field,
+        value: summary.min,
+      });
+      return {
+        histogram: undefined,
+        range,
+        unclippedRange: range,
+        unclippedRangeColor: globals.blue,
+        isSingleValue: true,
+        OK2Render: false,
+      };
+    }
+
+    const isSingleValue = summary.min === summary.max;
+    // if we are clipped, fetch both our value and our unclipped value,
+    // as we need the absolute min/max range, not just the clipped min/max.
     let unclippedRange = [...range];
     if (isClipped) {
       const parent = await annoMatrix.viewOf.fetch(...query);
@@ -643,7 +670,6 @@ class HistogramBrush extends React.PureComponent {
       this.height
     );
 
-    const isSingleValue = summary.min === summary.max;
     const nonFiniteExtent =
       summary.min === undefined ||
       summary.max === undefined ||