Google Sheets: Fill Down Data - google-apps-script

Question

I want to fill down Col D starting at Item Number Row and fill down that number to that row and the rows of data under it. And repeat for next items until done. Pictures below of desired results.
How would I do this in appscript?
Before:
Desired Result:

Answer 1

I believe your script as follows.
You want to achieve the situation from the top image to the bottom image in your question using Google Apps Script.
Flow:
In this case, I would like to propose the following flow.
Retrieve values from the sheet.
Create an array for putting values to the column "D".
In this case, I thought that the values for putting to the column "D" can be created using the retrieve values.
Put the values to the column "D".
Sample script:
When you use this script, please copy and paste the following script to the container-bound script of the Spreadsheet. And please set sheetName.
function myFunction() {
const sheetName = "Sheet1"; // Please set this.
// 1. Retrieve values from the sheet.
const sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName);
const values = sheet.getDataRange().getValues();
// 2. Create an array for putting values to the column "D".
let temp = 0;
const outputValues = values.map(([a, b]) => {
if (a.toUpperCase().includes("ITEM NUMBER:")) temp = b;
return [temp];
});
// 3. Put the values to the column "D".
sheet.getRange("D1:D" + outputValues.length).setValues(outputValues);
}
Note:
Please use this script with enabling V8.
If you want to use the script as the custom function, you can also use the following script. In this case, please put a custom function of =myFunction2(A1:B12) to the cell "D1" for your sample Spreadsheet.
function myFunction2(values) {
let temp = 0;
return values.map(([a, b]) => {
if (a.toUpperCase().includes("ITEM NUMBER:")) temp = b;
return [temp];
});
}
References:
getValues()
map()
setValues(values)