Auto number input to google spreadsheet using array - google-apps-script

Question

I have started studying GAS recently.
I wrote Auto number script using Low number.
There is spreadsheet has some datas, I want put A Column including batch ID number at one time.
function autoID() {
var sheet = SpreadsheetApp.getActiveSheet();
var lastrow = sheet.getLastRow();
for(i=1; i<= lastrow-1; i++)
{
var num = sheet.getRange(i,1);
num.setValue(i);
}
Browser.msgBox("This is end!");
}
This in no good example,it takes too much time.
I wonder I should use Array() ..
may be ↓　this is hint..
https://developers.google.com/apps-script/best_practices
But this Best Practices　doesn't work, I tried this...
function autoID() {
var sheet = SpreadsheetApp.getActiveSheet();
var lastrow = sheet.getLastRow();
var num = new Array();
idrange = sheet.getRamge("A2:A"+(lastrow-1));
idrange = idrange.getValues();
for(i=1; i<= lastrow-1; i++)
{
var num = sheet.getRange(i,1);
num[(i)]=i;
}
Browser.messageBox(num[1]); // this is 1;
idrange.setValues(num); // this is error
}
How is change type?
Please help me..
I think this must be so easy.

Answer 1

Not sure I understood exactly what you want to do but here is how it works without code errors :
function autoID() {
var sheet = SpreadsheetApp.getActiveSheet();
var lastrow = sheet.getLastRow();
var num = new Array();
var idrange = sheet.getRange("A2:A"+(lastrow));
var idrangeVal = idrange.getValues()
for(var i in idrangeVal){
num.push([i]);
}
idrange.setValues(num);
}
edit following your comment :
Here is a version the (I hope) does what you expected...
function autoID() {
var sheet = SpreadsheetApp.getActiveSheet();
var valuesInrangeA = sheet.getRange('A2:A').getValues();
var maxA = 0
for(var n=0 ;n<valuesInrangeA.length ; n++){
if(valuesInrangeA[n][0]!=''){maxA=n+2};
};
var num = new Array();
for(var i=1 ; i<maxA ; i++){
num.push([i]);
}
sheet.getRange("B2:B"+maxA).setValues(num);
}