Use more robust type narrowing for Measurement and Collection

As suggested in review

<#1910 (comment)>

src/actions/measurements.ts

@@ -14,14 +14,14 @@ import {
 } from "./types";
 import {
   Collection,
-  isCollection,
-  isMeasurement,
+  asCollection,
+  asMeasurement,
   isMeasurementsDisplay,
   measurementsDisplayValues,
   Measurement,
   MeasurementsDisplay,
   MeasurementsJson,
-  MeasurementsState
+  MeasurementsState,
 } from "../reducers/measurements/types";
 
 /**
@@ -311,12 +311,7 @@ const parseMeasurementsJSON = (json: MeasurementsJson): MeasurementsState => {
         }
       });
 
-
-      if (isMeasurement(parsedMeasurement)) {
-        return parsedMeasurement;
-      } else {
-        throw new Error("Could not parse a valid measurement");
-      }
+      return asMeasurement(parsedMeasurement);
     });
 
     // Create groupings Map for easier access of sorted values and to keep groupings ordering
@@ -340,11 +335,7 @@ const parseMeasurementsJSON = (json: MeasurementsJson): MeasurementsState => {
       })
     );
 
-    if (isCollection(collection)) {
-      return collection;
-    } else {
-      throw new Error("Could not parse a valid collection");
-    }
+    return asCollection(collection);
   });
 
   const collectionKeys = collections.map((collection) => collection.key);

src/reducers/measurements/types.ts

@@ -63,8 +63,16 @@ export interface Measurement {
   [key: string]: string | number
 }
 
-export function isMeasurement(x: any): x is Measurement {
-  return Boolean(x[measurementIdSymbol] !== undefined && x.strain && x.value !== undefined)
+export function asMeasurement(x: Partial<Measurement>): Measurement {
+  if (x[measurementIdSymbol] !== undefined && x.strain && x.value !== undefined) {
+    return {
+       ...x,
+       [measurementIdSymbol]: x[measurementIdSymbol],
+       strain: x.strain,
+       value: x.value,
+    }
+  }
+  throw new Error("Measurement is partial.");
 }
 
 export interface Collection {
@@ -80,15 +88,26 @@ export interface Collection {
   x_axis_label: string
 }
 
-export function isCollection(x: any): x is Collection {
-  return Boolean(
+export function asCollection(x: Partial<Collection>): Collection {
+  if (
     x.fields &&
     x.filters &&
     x.groupings &&
     x.key &&
     x.measurements &&
     x.x_axis_label
-  );
+  ){
+    return {
+      ...x,
+      fields: x.fields,
+      filters: x.filters,
+      groupings: x.groupings,
+      key: x.key,
+      measurements: x.measurements,
+      x_axis_label: x.x_axis_label,
+    }
+  }
+  throw new Error("Collection is partial.");
 }
 
 export interface MeasurementsState {