Pasting values in a different column depending on a Data Validation drop-down selection - arrays

Question

Suppose I have the following setting on a Google Sheet:
Column A containing a list of different items (Apple/Melon/Grapes), column B containing Data Validation drop-down menus with either option 1 or 2.
What I want is that if I select option 1 for any of the items, the value of the corresponding cell in column A is going to pasted in D2. If I select option 1 for another item, the value will be pasted in D3, and so forth, thus building a secondary list without leaving any blank cells in between. If I select option 2, the item should be ignored.
Ideally, the order of the items in column D would follow my actions chronologically, i.e. if the item in A3 is the first item I select option 1 for, then it shall be on the top of the column D list at all times, even if later on I select option 1 for A1 as well (which shall then sit on the second position of the D list).
Is it possible to be achieved?

Answer 1

You can do this via Apps Script with a simple onEdit trigger, using its event object.
Select Tools > Script editor to open the Apps Script editor.
Copy this function and save the project (check inline comments):
function onEdit(e) {
// Get the range that was edited (column, row, sheet, value):
var range = e.range;
var sheet = range.getSheet();
var col = range.getColumn();
var row = range.getRow();
var value = range.getValue();
var sheetName = "Sheet1"; // Name of your sheet (the tab) (please change if necessary)
// Check that edited column is B, edited value is 1, and edited sheet is "Sheet1":
if (sheet.getName() === sheetName && col === 2 && value === 1) {
// Get length of non-empty cells in column D:
var columnD = sheet.getRange("D:D").getValues().map(function(item) {
return item[0];
}).filter(function(item) {
return item !== "";
});
var firstEmptyRow = columnD.length + 1; // First empty row in column D
var itemToCopy = sheet.getRange(row, 1).getValue(); // Get value from column A to copy
sheet.getRange(firstEmptyRow, 4).setValue(itemToCopy); // Write value to column D
}
}
Now, every time you edit column B and the edited value is 1, the corresponding option from column A will get copied to column D.
Reference:
onEdit
Event objects: Edit

Answer 2

delete range D2:D and paste in D2 cell:
=FILTER(A:A; B:B=1)