refactor heatmap convertColumnData

Author: archmoj

src/traces/heatmap/convert_column_xyz.js

@@ -30,18 +30,21 @@ module.exports = function convertColumnData(trace, ax1, ax2, var1Name, var2Name,
     var text;
     var hovertext;
 
+    var nI = col2vals.length;
+    var nJ = col1vals.length;
+
     for(i = 0; i < arrayVarNames.length; i++) {
-        newArrays[i] = Lib.init2dArray(col2vals.length, col1vals.length);
+        newArrays[i] = Lib.init2dArray(nI, nJ);
     }
 
     if(hasColumnText) {
-        text = Lib.init2dArray(col2vals.length, col1vals.length);
+        text = Lib.init2dArray(nI, nJ);
     }
     if(hasColumnHoverText) {
-        hovertext = Lib.init2dArray(col2vals.length, col1vals.length);
+        hovertext = Lib.init2dArray(nI, nJ);
     }
 
-    var after2before = Lib.init2dArray(col2vals.length, col1vals.length);
+    var after2before = Lib.init2dArray(nI, nJ);
 
     for(i = 0; i < colLen; i++) {
         if(col1[i] !== BADNUM && col2[i] !== BADNUM) {