Merge pull request #1555 from hy9be/perf-scatterlayersort

Optimize the performance of scatter trace sorting comparator with map

Author: etpinard

src/traces/scatter/plot.js

@@ -51,13 +51,13 @@ module.exports = function plot(gd, plotinfo, cdscatter, transitionOpts, makeOnCo
     // Sort the traces, once created, so that the ordering is preserved even when traces
     // are shown and hidden. This is needed since we're not just wiping everything out
     // and recreating on every update.
-    for(i = 0, uids = []; i < cdscatter.length; i++) {
-        uids[i] = cdscatter[i][0].trace.uid;
+    for(i = 0, uids = {}; i < cdscatter.length; i++) {
+        uids[cdscatter[i][0].trace.uid] = i;
     }
 
     scatterlayer.selectAll('g.trace').sort(function(a, b) {
-        var idx1 = uids.indexOf(a[0].trace.uid);
-        var idx2 = uids.indexOf(b[0].trace.uid);
+        var idx1 = uids[a[0].trace.uid];
+        var idx2 = uids[b[0].trace.uid];
         return idx1 > idx2 ? 1 : -1;
     });