1diff --git a/README.md b/README.md
 2index 5ecc9a2..2c58574 100644
 3--- a/README.md
 4+++ b/README.md
 5@@ -3,3 +3,9 @@ TypeScript implementation of a spreadsheet.
 6 
 7 ## TODO
 8 Things I should do.
 9+
10+### Rename anything referencing an "item"
11+
12+### `setValue()`, `getValue()` on a sheet
13+
14+## `load()` array of array of values for a sheet
15diff --git a/src/Sheet.ts b/src/Sheet.ts
16index 596e093..8e5da10 100644
17--- a/src/Sheet.ts
18+++ b/src/Sheet.ts
19@@ -44,14 +44,12 @@ var Sheet = (function () {
20   };
21 
22   class Matrix {
23-    public data: Array<Cell>;
24+    public data: Object;
25     constructor() {
26-      this.data = [];
27+      this.data = {};
28     }
29     getItem(key: A1CellKey) {
30-      return this.data.filter(function (cell) {
31-        return cell.id === key.toString();
32-      })[0];
33+      return this.data[key.toString()];
34     }
35     addItem(cell: Cell) {
36       var cellId = cell.id;
37@@ -61,12 +59,8 @@ var Sheet = (function () {
38       cell.row = coords.row;
39       cell.col = coords.col;
40 
41-      var existingCell = this.data.filter(function (cell) {
42-        return cell.id === cellId;
43-      })[0];
44-
45-      if (!existingCell) {
46-        this.data.push(cell);
47+      if (!(cellId in this.data)) {
48+        this.data[cellId] = cell;
49       } else {
50         this.getItem(key).updateDependencies(cell.dependencies);
51         this.getItem(key).setValue(cell.value);
52@@ -77,11 +71,15 @@ var Sheet = (function () {
53     }
54     getDependencies(id: string) {
55       var getDependencies = function (id: string) {
56-        var filtered = this.data.filter(function (cell) {
57-          if (cell.deps) {
58-            return cell.deps.indexOf(id) > -1;
59+        var filtered = [];
60+        for (var key in this.data) {
61+          var cell = this.data[key];
62+          if (cell.dependencies) {
63+            if (cell.dependencies.indexOf(id) > -1) {
64+              filtered.push(cell)
65+            }
66           }
67-        });
68+        }
69 
70         var deps = [];
71         filtered.forEach(function (cell) {
72@@ -132,9 +130,9 @@ var Sheet = (function () {
73           recalculateCellDependencies(cell);
74         }
75       }
76-      this.data.forEach(function (item) {
77-        console.log(item.id, item.formula, item.value);
78-      });
79+      for (var key in this.data) {
80+        console.log(this.data[key].id, this.data[key].formula, this.data[key].value);
81+      }
82     }
83   }
84