Array of column Letters to Array of Column Numbers not working - google-apps-script

Question

This is more or less my first attempt at writing a Javascript function and I want to convert an array of column numbers to an array of column letters
If I run testFunction I get undefined
function testFunction() {
var ui = SpreadsheetApp.getUi();
aryCLTCN(["A","C","D"])
ui.alert(aryCLTCN[3]);
}
function aryCLTCN(array) {
var columnLet = array
var output = [];
for (var i = 0, length = columnLet.length; i < length; i++) {
output[i] = [];
output[i] = CLTCN(columnLet[(i)]);
}
}
function CLTCN(letter)
{
var column = 0, length = letter.length;
for (var i = 0; i < length; i++)
{
column += (letter.charCodeAt(i) - 64) * Math.pow(26, length - i - 1);
}
return column;
}

Answer 1

There are several problems with your code.
Within function testFunction() you call aryCLTCN(["A","C","D"]) but don't assign the result to a variable, then with aryCLTCN[3] you are trying to access a property "3" of the function itself. Which isn't a syntax error because functions can have properties, but the function has no such property so you get undefined. You need something like this:
var result = aryCLTCN(["A","C","D"]);
ui.alert(result[3]);
Except note that JavaScript arrays are zero-based, which means that [3] tries to access the fourth element, but your array only has three elements.
Within function aryCLTCN(array) you create an output array but don't return it. You need to add return output;.
Also with these two lines:
output[i] = [];
output[i] = CLTCN(columnLet[(i)]);
...the first line assigns output[i] to a new empty array, but the second line overwrites that with the return value from CLTCN(columnLet[(i)]);. You can remove output[i] = [];.
Putting all that together:
function testFunction() {
// var ui = SpreadsheetApp.getUi(); // commented out for demo in browser
var result = aryCLTCN(["A","C","D"])
// using alert() instead of ui.alert() for demo here in browser
alert(result[3]); // undefined because there's no 4th element
alert(result[2]); // shows third element
}
function aryCLTCN(array) {
var columnLet = array
var output = [];
for (var i = 0, length = columnLet.length; i < length; i++) {
output[i] = CLTCN(columnLet[(i)]);
}
return output;
}
function CLTCN(letter)
{
var column = 0, length = letter.length;
for (var i = 0; i < length; i++)
{
column += (letter.charCodeAt(i) - 64) * Math.pow(26, length - i - 1);
}
return column;
}
testFunction();
(Note that for the purposes of having a runnable code snippet in my answer I'm using alert() instead of ui.alert(), but in your real code you would stick with ui.alert().)

Answer 2

You get an undefined error because you are calling the trying to access an index on a function. aryCLTCN function needs to have a return the output array and you need to assign it to a variable in your testFunction to be able to access its elements.
Although there was nothing logically or effectively wrong with your functions, I have provided another working solution below.
function testFunction() {
var ui = SpreadsheetApp.getUi();
var colArr = ["A", "B", "Z", "AA", "AZ", "ZA", "AAA"];
var nColArr = colArr.map(function(col) {
var colNum = 0;
col.split('').forEach(function(l, i) { colNum += (l.charCodeAt() - 64) * Math.pow(26, col.length - 1 - i) });
return colNum;
});
ui.alert(nColArr); //Shows all elements inside the nColArr array.
ui.alert(nColArr[3]); //Shows the 4th element inside the nColArr array.
}
Try it out:
var colArr = ["A", "B", "Z", "AA", "AZ", "ZA", "AAA"];
var nColArr = colArr.map(function(col) {
var colNum = 0;
col.split('').forEach(function(l, i) {
colNum += (l.charCodeAt() - 64) * Math.pow(26, col.length - 1 - i)
});
return colNum;
});
console.log(nColArr);