improve performance around category highlighting (#849)

* remove function call and add comment

* separate crossfilter size calc into memoized function

client/src/components/graph/graph.js

@@ -52,16 +52,27 @@ class Graph extends React.Component {
     return colors;
   });
 
+  computePointSizesFromCrossfilter = memoize((len, crossfilter) => {
+    const sizes = new Float32Array(len);
+    crossfilter.fillByIsSelected(sizes, 4, 0.2);
+
+    return sizes;
+  });
+
   computePointSizes = memoize(
     (len, crossfilter, metadataField, categoryField) => {
       /*
     compute webgl dot size for each point
     */
 
-      const sizes = new Float32Array(len);
-      crossfilter.fillByIsSelected(sizes, 4, 0.2);
+      const selectionSizes = this.computePointSizesFromCrossfilter(
+        len,
+        crossfilter
+      );
+      let sizes;
 
       if (metadataField && categoryField) {
+        sizes = selectionSizes.slice();
         const valuesArr = crossfilter.data.col(metadataField).asArray();
 
         for (let i = 0; i < len; i += 1) {
@@ -69,6 +80,8 @@ class Graph extends React.Component {
             sizes[i] = 10;
           }
         }
+      } else {
+        sizes = selectionSizes;
       }
       return sizes;
     }