change mapById, groupById to match the writeup (omit undefined)

README.md

@@ -123,6 +123,7 @@ array.  The value is `undefined` if the property is not set.
 
 Map the objects by a property value.  Returns a hash mapping each value to the
 first object whose `idName` is set to that value.  Null and undefined objects are skipped.
+Objects that do not have that property are skipped.
 Id values should be strings or numbers.  Returns the target object, which is `{}` by default.
 
     var items = [{ id: 'a', v: 1 }, { id: 'b' }, { id: 'a', v: 2 }, { v: 3 }];
@@ -132,7 +133,7 @@ Id values should be strings or numbers.  Returns the target object, which is `{}
 ### qibl.groupById( items, idName [,target] )
 
 Similar to `mapById`, but group objects by property value into arrays.  Returns a mapping
-of ids to lists of objects.
+of ids to lists of objects.  Objects that do not have the `idName` property set are omitted.
 
     var items = [{ id: 'a', v: 1 }, { id: 'b' }, { id: 'a', v: 2 }, { v: 3 }];
     qibl.mapById(items, 'id')

qibl.js

@@ -509,6 +509,7 @@ function _mapById( arrayOfObjects, idName, target, all ) {
         var obj = arrayOfObjects[i];
         if (obj == undefined) continue;
         var key = obj[idName];
+        if (key === undefined) continue;
         (!all) ? target[key] = obj : (target[key]) ? target[key].push(obj) : target[key] = new Array(obj);
     }
     return target;

test-qibl.js

@@ -999,15 +999,15 @@ module.exports = {
             t.deepEqual(qibl.mapById([{a:1}, {a:2}], 'a'), {1: {a:1}, 2: {a:2}});
             t.deepEqual(qibl.mapById([{a:1}, {a:2, b:2}], 'a'), {1: {a:1}, 2: {a:2, b:2}});
 
-            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'a'), {1: {a:1}, 'undefined': {b:2}});
-            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'b'), {2: {b:2}, 'undefined': {a:1}});
-            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'c'), {'undefined': {b:2}});
+            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'a'), {1: {a:1}});
+            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'b'), {2: {b:2}});
+            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'c'), {});
 
             t.deepEqual(qibl.mapById([], 'a'), {});
-            t.deepEqual(qibl.mapById([,,,null,undefined,,,7,false,0,"string"], 'a'), {'undefined': "string"});
+            t.deepEqual(qibl.mapById([,,,null,undefined,,,7,false,0,"string"], 'a'), {});
             t.deepEqual(qibl.mapById([,,{a:1}], 'a'), {1: {a:1}});
 
-            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'a', {x:9}), {x:9, 1: {a:1}, 'undefined': {b:2}});
+            t.deepEqual(qibl.mapById([{a:1}, {b:2}], 'a', {x:9}), {x:9, 1: {a:1}});
 
             t.done();
         },
@@ -1016,8 +1016,8 @@ module.exports = {
     'groupById': {
         'should return arrays of objects': function(t) {
             var a1 = {a:1}, a2 = {a:2}, b1 = {b:1};
-            t.deepEqual(qibl.groupById([a1, a2, a1, b1], 'a'), {1: [a1, a1], 2: [a2], 'undefined': [b1]});
-            t.deepEqual(qibl.groupById([a1, b1], 'c'), {'undefined': [a1, b1]});
+            t.deepEqual(qibl.groupById([a1, a2, a1, b1], 'a'), {1: [a1, a1], 2: [a2]});
+            t.deepEqual(qibl.groupById([a1, b1], 'c'), {});
             t.done();
         },
     },