Convert between characters and numbers

lib/index.js

@@ -338,6 +338,39 @@ module.exports = (function() {
         });
     };
 
+    // Turn a reference like "AA" into a number like 27
+    Workbook.prototype.charToNum = function(str) {
+        var num = 0;
+        for(var idx = str.length - 1, iteration = 0; idx >= 0; --idx, ++iteration) {
+            var thisChar = str.charCodeAt(idx) - 64, // A -> 1; B -> 2; ... Z->26
+                multiplier = Math.pow(26, iteration);
+            num += multiplier * thisChar;
+        }
+        return num;
+    };
+
+    // Turn a number like 27 into a reference like "AA"
+    Workbook.prototype.numToChar = function(num) {
+        var str = "";
+
+
+        for(var i = 0; num > 0; ++i) {
+            var remainder = num % 26,
+                charCode = remainder + 64;
+            num = (num - remainder) / 26;
+
+            // Compensate for the fact that we don't represent zero, e.g. A = 1, Z = 26, but AA = 27
+            if(remainder === 0) { // 26 -> Z
+                charCode = 90;
+                --num;
+            }
+
+            str = String.fromCharCode(charCode) + str;
+        }
+
+        return str;
+    };
+
     Workbook.prototype.stringify = function (value) {
         var self = this;
 

test/helpers-test.js

@@ -236,6 +236,62 @@ describe("Helpers", function() {
 
     });
 
+    describe('charToNum', function() {
+
+        it("can return single letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.charToNum("A")).toEqual(1);
+            expect(t.charToNum("B")).toEqual(2);
+            expect(t.charToNum("Z")).toEqual(26);
+        });
+
+        it("can return double letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.charToNum("AA")).toEqual(27);
+            expect(t.charToNum("AZ")).toEqual(52);
+            expect(t.charToNum("BZ")).toEqual(78);
+        });
+
+        it("can return triple letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.charToNum("AAA")).toEqual(703);
+            expect(t.charToNum("AAZ")).toEqual(728);
+            expect(t.charToNum("ADI")).toEqual(789);
+        });
+
+    });
+
+    describe('numToChar', function() {
+
+        it("can convert single letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.numToChar(1)).toEqual("A");
+            expect(t.numToChar(2)).toEqual("B");
+            expect(t.numToChar(26)).toEqual("Z");
+        });
+
+        it("can convert double letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.numToChar(27)).toEqual("AA");
+            expect(t.numToChar(52)).toEqual("AZ");
+            expect(t.numToChar(78)).toEqual("BZ");
+        });
+
+        it("can convert triple letter numbers", function() {
+            var t = new XlsxTemplate();
+            
+            expect(t.numToChar(703)).toEqual("AAA");
+            expect(t.numToChar(728)).toEqual("AAZ");
+            expect(t.numToChar(789)).toEqual("ADI");
+        });
+
+    });
+
     describe('stringify', function() {
 
         it("can stringify dates", function() {