Fixed and added test for blend method.

.gitignore

@@ -0,0 +1,4 @@
+.DS_Store
+Thumbs.db
+node_modules
+*.tmp*

blend.js

@@ -16,10 +16,12 @@ module.exports = function(grids, options){
 function merge(a, b){
 	var grid_c = [];
 	var data_c = {};
+	var keys_c = [""];
+	var key = 1;
+	var key_mapping_a = {};
+	var key_mapping_b = {};
 
 	var dim = a.grid.length;
-	var offset = b.keys.length;
-
 	for(var y = 0; y < dim; y++){
 		var row_a = a.grid[y];
 		var row_b = b.grid[y];
@@ -28,22 +30,37 @@ function merge(a, b){
 			var id_a = decode(row_a.charCodeAt(x));
 			var id_b = decode(row_b.charCodeAt(x));
 			var id_c = 0;
-			if(b.data[id_b]){
-				id_c = id_b;
-				data_c[id_c] = b.data[id_b];
-			} else if (a.data[id_a]) {
-				id_c = id_a + offset;
-				data_c[id_c] = a.data[id_a];
+			var key_a = a.keys[id_a];
+			var key_b = b.keys[id_b];
+			var key_c = 0;
+			if(b.data[key_b]){
+				key_c = key_mapping_b[key_b];
+				if(!key_c) {
+					key_c = (key++).toString();
+					key_mapping_b[key_b] = key_c;
+					keys_c.push(key_c);
+				}
+				data_c[key_c] = b.data[key_b];
+				id_c = keys_c.indexOf(key_c);
+			} else if (a.data[key_a]) {
+				key_c = key_mapping_a[key_a];
+				if(!key_c) {
+					key_c = (key++).toString();
+					key_mapping_a[key_a] = key_c;
+					keys_c.push(key_c);
+				}
+				data_c[key_c] = a.data[id_a];
+				id_c = keys_c.indexOf(key_c);
 			}
 			row_c.push(encode(id_c));
 		}
-		grid_c.push(row.join(''));
+		grid_c.push(row_c.join(''));
 	}
 
 	return {
 		grid: grid_c,
 		data: data_c,
-		keys: Object.keys(data_c)
+		keys: keys_c
 	};
 }
 

test/blend.test.js

@@ -0,0 +1,18 @@
+var blend = require('../blend.js');
+var assert = require('chai').assert;
+
+function assertGridEqual(result, expected){
+	assert.deepEqual(result.keys, expected.keys, 'keys should match');
+	for(var i = 0; i < expected.grid.length; i++){
+		assert.equal(result.grid[i], expected.grid[i], 'row '+i+' should match');
+	};
+	assert.deepEqual(result.data, expected.data, 'data property should match');
+}
+
+describe('blend()', function() {
+	it('should merge utfgrids', function() {
+		var fixture = require('./fixtures/a.js');
+		var output = blend(fixture.inputs);
+		assertGridEqual(output, fixture.result);
+	});
+});

test/fixtures/a.js

@@ -0,0 +1,65 @@
+module.exports.inputs = [{
+	"data": {
+		"1": {"id": 1},
+		"2": {"id": 2},
+		"3": {"id": 3},
+		"4": {"id": 4},
+		"5": {"id": 5},
+		"6": {"id": 6}
+	},
+	"keys": ["","1","2","3","4","5","6"],
+	"grid": [
+		"        ",
+		"        ",
+		"        ",
+		"        ",
+		"   !#$  ",
+		"   %&'  ",
+		"        ",
+		"        "
+	]
+},{
+	"data": {
+		"1": {"id": 7},
+		"2": {"id": 8},
+		"3": {"id": 9},
+		"4": {"id": 10},
+		"5": {"id": 11},
+		"6": {"id": 12}
+	},
+	"keys": ["","1","2","3","4","5","6"],
+	"grid": [
+		"        ",
+		"        ",
+		"        ",
+		"        ",
+		"        ",
+		"   !#$  ",
+		"   %&'  ",
+		"        "
+	]
+}];
+module.exports.result = {
+	"data": {
+		"1": {"id": 1},
+		"2": {"id": 2},
+		"3": {"id": 3},
+		"4": {"id": 7},
+		"5": {"id": 8},
+		"6": {"id": 9},
+		"7": {"id": 10},
+		"8": {"id": 11},
+		"9": {"id": 12},
+	},
+	"keys": ["","1","2","3","4","5","6","7","8","9"],
+	"grid": [
+		"        ",
+		"        ",
+		"        ",
+		"        ",
+		"   !#$  ",
+		"   %&'  ",
+		"   ()*  ",
+		"        "
+	]
+};