Need a more efficient solution than looping - optimization

Question

I am building a spreadsheet that tracks work in progress as it moves through steps of a manufacturing process.
Each step of the process has a column with the total parts moved to each stage. To the left of this column is a column for number of parts moved to the stage (parts move through a few at a time).
My scrpit then takes the values in the "add" column, adds them to the "total" column, then reset the "add" column to "".
Here's the code:
function addColumns() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
// ss is now the spreadsheet the script is associated with
var sheet = ss.getSheets()[0]; // sheets are counted starting from 0
// sheet is the first worksheet in the spreadsheet
for (var i=4; i<500; i++ ) {
if(sheet.getRange(i,1).getValue()>0){ //Only run if order number not empty
//Breakout Column
var add = sheet.getRange(i,6);
var total = sheet.getRange(i,7);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
//CNC Column
var add = sheet.getRange(i,8);
var total = sheet.getRange(i,9);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
//CutSand Column
var add = sheet.getRange(i,10);
var total = sheet.getRange(i,11);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
//Lasered Column
var add = sheet.getRange(i,12);
var total = sheet.getRange(i,13);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
//To Finishing Column
var add = sheet.getRange(i,14);
var total = sheet.getRange(i,15);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
// Defective Column
var add = sheet.getRange(i,17);
var total = sheet.getRange(i,18);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
//Etsy Column
var add = sheet.getRange(i,20);
var total = sheet.getRange(i,21);
total.setValue(total.getValue() + add.getValue());
add.setValue("");
}
if(sheet.getRange(i,4).getValue()<1){i=500} //Once you find a blank order exit the loop
}
}
My code as written does accomplish this; it does exactly what I need. The problem is that since the code is accessing the spreadsheet on each loop it takes almost a full second per cell to run, and with 7 steps per order it can take minutes at a time to run through with lots of orders...
This is a pretty simple mathematical task, so there has to be a more efficient way of doing it, I just haven't been able to find the right keywords to describe what I need to do.
I am quite happy to learn whatever needs to be done, just need to know what direction to head.
Thanks in advance!

Answer 1

I would suggest to do something like this: (not tested)
function addColumns() {
var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheets()[0]; // Refers to the first worksheet in the spreadsheet
var data = sheet.getDataRange().getValues(); // Acquires all values of the sheet
for (var i = 3; i < data.length; i++) { // Loop over every row
if (data[i][0].length > 0) { // Check if first column has a value
// Breakout
sheet.getRange(i+1,7).setValue(parseFloat(data[i][6]) + parseFloat(data[i][5]));
sheet.getRange(i+1,6).clear();
// Repeat code above for other columns
}
}
}
This code acquires all the data from the sheet instead of looping over a fixed amount of 500 rows. Assuming that your data starts at row 4, I've implemented this in the code above as well.
Variable data acquires all the data at one moment instead of trying to fetch values of every range (cell) all the time. I expect that this will save your script quite some time.
Because we acquire the data at once, the script sees the value as a string. Before we calculate the new value of the total column, we parse the value as a float (a number with decimals).
The code above is not tested as I don't have a sheet ready in the same format as you do but I think the logic is clear and if it doesn't work I suppose you should be able to adjust it to work for your sheet.