(core) Fix bar chart weirdness when x axis has redundant values

Summary:
Bar chart was a bit broken when there were redundant values on the X axis: the bars’s height maps to the sum of all the corresponding y values, when the data that shows up on hover is only the last one.

It seems that plotly does not support redundant values in the x axis and in all Plotly examples (implementation relies on plotly) x values only have unique values.

This diff, fixes by making sure x axis has unique values. If user actually wants to plot groups, they'll have to use a summary charts.

Test Plan: tested manually

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3011

app/client/lib/chartUtil.ts

@@ -1,5 +1,7 @@
 import {typedCompare} from 'app/common/SortFunc';
 import {Datum} from 'plotly.js';
+import range = require('lodash/range');
+import uniqBy = require('lodash/uniqBy');
 
 /**
  * Sort all values in a list of series according to the values in the first one.
@@ -18,3 +20,14 @@ export function sortByXValues(series: Array<{values: Datum[]}>): void {
     s.values = indices.map((i) => values[i]);
   }
 }
+
+// creates new version of series that has a duplicate free version of the values in the first one.
+export function uniqXValues<T extends {values: Datum[]}>(series: Array<T>): Array<T> {
+  if (!series[0]) { return []; }
+  const n = series[0].values.length;
+  const indexToKeep = new Set(uniqBy(range(n), (i) => series[0].values[i]));
+  return series.map((line: T) => ({
+    ...line,
+    values: line.values.filter((_val, i) => indexToKeep.has(i))
+  }));
+}