Setting a column to equal the negative of a row in Google Sheets - google-sheets

Question

The Google Sheets API seems vague and I'm probably just too tired.
function onEdit(e) {
var sheet = SpreadsheetApp.getActiveSpreadsheet();
var positives = sheet.getRange("D3:AG3");
var negatives = sheet.getRange("C4:C33");
for (i=0;i<positives.getLastColumn();i++) {
var j = positives[i]*-1;
negatives[i].setValue(j);
}
}
I'm sure I'm doing eight things wrong but if someone is more familiar with Google Sheets, please throw a brick at me.

Answer 1

First, positives is a ranges, and you need to use getValues() to get an array that you can manipulate.
Second, it's not recommended to use Sheets API methods inside loops, the best practice is to manipulate arrays in loops and then use single get and set values API to read / write to a range.
Sample Code:
function onEdit(e) {
var sheet = SpreadsheetApp.getActiveSpreadsheet();
var positives = sheet.getRange("D3:AG3").getValues();
var negatives = sheet.getRange("C4:C33");
var result = [];
for (i = 0; i < positives[0].length; i++) {
result.push([positives[0][i] * -1]);
}
negatives.setValues(result);
}
Sample Output: (I only put values in three rows)
Reference:
push()

Answer 2

Avoid using onEdit for these kind of changes as it will be resource intensive. You are changing all the values of the column into negative of the row EVERY TIME you edit the sheet (Unless that should be the case)
If you really want to use onEdit, be sure to limit it only when the specific range is edited.
Code:
function onEdit(e) {
const row = e.range.getRow();
const column = e.range.getColumn();
// if edited range is within D3:AG3
if(row == 3 && column >= 4 && column <= 33) {
// write to the corresponding row (invert col and row)
e.source.getActiveSheet().getRange(column, row).setValue(e.value * -1);
}
}
Note:
Behaviour of the onEdit function is that when you edit the range D3:AG3, it will negate its value and write into its corresponding destination, one by one.
If you edit D3, it will assign that negative value into C4, nothing more.
If you edit outside the positive range, it will not do anything.
Another approach is to copy your positive row into negative column by transforming your data structure into the destination by bulk.
Code:
function rowToColumn() {
var sheet = SpreadsheetApp.getActiveSpreadsheet();
var pRange = sheet.getRange("D3:AG3");
var pValues = pRange.getValues();
// pValues is a 2D array now
// row range values = [[1, 2, 3, ...]
var negatives = sheet.getRange("C4:C33");
// column range values = [[1], [2], [3], ...]
// since structure of row is different than column
// one thing we can do is convert the row into column structure
// and multiply each element with -1, then assign to negatives
pValues = pValues.map(function(item) {
item = item.map(function(col) {
return [col * -1];
});
return item;
})[0];
// set values into the negatives range
negatives.setValues(pValues);
}
Note:
Behaviour of the rowToColumn function is that it transfers all the values of the row range and then put it into negatives range all at once.
Blank cells will yield 0 by default, add a condition on return [col * -1]; if you want blank cells to return other values instead.
Output: