multiple selections on parcoords axes

src/lib/coerce.js

@@ -260,9 +260,11 @@ exports.valObjectMeta = {
             'An {array} of plot information.'
         ].join(' '),
         requiredOpts: ['items'],
-        // set dimensions=2 for a 2D array
+        // set `dimensions=2` for a 2D array or '1-2' for either
         // `items` may be a single object instead of an array, in which case
         // `freeLength` must be true.
+        // if `dimensions='1-2'` and items is a 1D array, then the value can
+        // either be a matching 1D array or an array of such matching 1D arrays
         otherOpts: ['dflt', 'freeLength', 'dimensions'],
         coerceFunction: function(v, propOut, dflt, opts) {
 
@@ -278,7 +280,7 @@ exports.valObjectMeta = {
                 return out;
             }
 
-            var twoD = opts.dimensions === 2;
+            var twoD = opts.dimensions === 2 || (opts.dimensions === '1-2' && Array.isArray(v) && Array.isArray(v[0]));
 
             if(!Array.isArray(v)) {
                 propOut.set(dflt);
@@ -288,19 +290,28 @@ exports.valObjectMeta = {
             var items = opts.items;
             var vOut = [];
             var arrayItems = Array.isArray(items);
-            var len = arrayItems ? items.length : v.length;
+            var arrayItems2D = arrayItems && twoD && Array.isArray(items[0]);
+            var innerItemsOnly = twoD && arrayItems && !arrayItems2D;
+            var len = (arrayItems && !innerItemsOnly) ? items.length : v.length;
 
-            var i, j, len2, vNew;
+            var i, j, row, item, len2, vNew;
 
             dflt = Array.isArray(dflt) ? dflt : [];
 
             if(twoD) {
                 for(i = 0; i < len; i++) {
                     vOut[i] = [];
-                    var row = Array.isArray(v[i]) ? v[i] : [];
-                    len2 = arrayItems ? items[i].length : row.length;
+                    row = Array.isArray(v[i]) ? v[i] : [];
+                    if(innerItemsOnly) len2 = items.length;
+                    else if(arrayItems) len2 = items[i].length;
+                    else len2 = row.length;
+
                     for(j = 0; j < len2; j++) {
-                        vNew = coercePart(row[j], arrayItems ? items[i][j] : items, (dflt[i] || [])[j]);
+                        if(innerItemsOnly) item = items[j];
+                        else if(arrayItems) item = items[i][j];
+                        else item = items;
+
+                        vNew = coercePart(row[j], item, (dflt[i] || [])[j]);
                         if(vNew !== undefined) vOut[i][j] = vNew;
                     }
                 }

src/traces/parcoords/attributes.js

@@ -43,6 +43,8 @@ module.exports = {
             editType: 'calc',
             description: 'The shown name of the dimension.'
         },
+        // TODO: better way to determine ordinal vs continuous axes,
+        // so users can use tickvals/ticktext with a continuous axis.
         tickvals: extendFlat({}, axesAttrs.tickvals, {editType: 'calc'}),
         ticktext: extendFlat({}, axesAttrs.ticktext, {editType: 'calc'}),
         tickformat: {
@@ -79,16 +81,26 @@ module.exports = {
         constraintrange: {
             valType: 'info_array',
             role: 'info',
+            freeLength: true,
+            dimensions: '1-2',
             items: [
                 {valType: 'number', editType: 'calc'},
                 {valType: 'number', editType: 'calc'}
             ],
             editType: 'calc',
             description: [
                 'The domain range to which the filter on the dimension is constrained. Must be an array',
-                'of `[fromValue, toValue]` with finite numbers as elements.'
+                'of `[fromValue, toValue]` with `fromValue <= toValue`, or if `multiselect` is not',
+                'disabled, you may give an array of arrays, where each inner array is `[fromValue, toValue]`.'
             ].join(' ')
         },
+        multiselect: {
+            valType: 'boolean',
+            dflt: true,
+            role: 'info',
+            editType: 'calc',
+            description: 'Do we allow multiple selection ranges or just a single range?'
+        },
         values: {
             valType: 'data_array',
             role: 'info',