add axis.matches boolean to splom dims

- defaults to `false`, when set to `true`,
  the generated splom axes will match

src/plots/cartesian/constraints.js

@@ -20,6 +20,9 @@ var FROM_BL = require('../../constants/alignment').FROM_BL;
 exports.handleConstraintDefaults = function(containerIn, containerOut, coerce, allAxisIds, layoutOut) {
     var constraintGroups = layoutOut._axisConstraintGroups;
     var matchGroups = layoutOut._axisMatchGroups;
+    var axId = containerOut._id;
+    var axLetter = axId.charAt(0);
+    var splomStash = ((layoutOut._splomAxes || {})[axLetter] || {})[axId] || {};
     var thisID = containerOut._id;
     var letter = thisID.charAt(0);
 
@@ -36,7 +39,7 @@ exports.handleConstraintDefaults = function(containerIn, containerOut, coerce, a
         }
     }, 'constraintoward');
 
-    if(!containerIn.scaleanchor && !containerIn.matches) return;
+    if(!containerIn.scaleanchor && !containerIn.matches && !splomStash.matches) return;
 
     var opts = getConstraintOpts(constraintGroups, thisID, allAxisIds, layoutOut);
 
@@ -50,7 +53,8 @@ exports.handleConstraintDefaults = function(containerIn, containerOut, coerce, a
     var matches = Lib.coerce(containerIn, containerOut, {
         matches: {
             valType: 'enumerated',
-            values: opts.linkableAxes
+            values: opts.linkableAxes,
+            dflt: splomStash.matches
         }
     }, 'matches');
 

src/traces/splom/attributes.js

@@ -100,6 +100,20 @@ module.exports = {
                 ].join(' ')
             },
 
+            // TODO make 'true' the default in v2?
+            matches: {
+                valType: 'boolean',
+                dflt: false,
+                role: 'info',
+                editType: 'calc',
+                description: [
+                    'Determines whether or not the x & y axes generated by this',
+                    'dimension match.',
+                    'Equivalent to setting the `matches` axis attribute in the layout',
+                    'with the correct axis id.'
+                ].join(' ')
+            },
+
             editType: 'calc+clearAxisTypes'
         },
 

src/traces/splom/defaults.js

@@ -63,6 +63,7 @@ function dimensionDefaults(dimIn, dimOut) {
     else coerce('visible');
 
     coerce('axis.type');
+    coerce('axis.matches');
 }
 
 function handleAxisDefaults(traceIn, traceOut, layout, coerce) {
@@ -97,7 +98,7 @@ function handleAxisDefaults(traceIn, traceOut, layout, coerce) {
     var xList = [];
     var yList = [];
 
-    function fillAxisStashes(axId, dim, list) {
+    function fillAxisStashes(axId, counterAxId, dim, list) {
         if(!axId) return;
 
         var axLetter = axId.charAt(0);
@@ -111,7 +112,8 @@ function handleAxisDefaults(traceIn, traceOut, layout, coerce) {
             if(dim) {
                 s.label = dim.label || '';
                 if(dim.visible && dim.axis) {
-                    s.type = dim.axis.type;
+                    if(dim.axis.type) s.type = dim.axis.type;
+                    if(dim.axis.matches) s.matches = counterAxId;
                 }
             }
         }
@@ -136,8 +138,8 @@ function handleAxisDefaults(traceIn, traceOut, layout, coerce) {
             undefined :
             yaxes[i];
 
-        fillAxisStashes(xaId, dim, xList);
-        fillAxisStashes(yaId, dim, yList);
+        fillAxisStashes(xaId, yaId, dim, xList);
+        fillAxisStashes(yaId, xaId, dim, yList);
         diag[i] = [xaId, yaId];
     }