Google scripts search single column and edit row based on result - google-apps-script

Question

I am trying to make a script button that will iterate through all rows and simply subtract cell G from cell E if G has a numerical value in it, then clear cell G.
I am having issues with trying to get only column G to see if it contains a numerical value, normally column G will be blank
I have tried getting the range specified but it is not sticking to the G column and is going everywhere. And I think I am probably not going about this the proper way. Right now I am just trying to get the cells with data in the G column to highlight so I know if I am even searching the right cells
function calculate() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();
var rangeData = sheet.getDataRange();
var lastColumn = rangeData.getLastColumn();
var lastRow = rangeData.getLastRow();
var searchRange = sheet.getRange("G1:G300");
var substring = "";
// Get array of values in the search Range
var rangeValues = searchRange.getValues();
// Loop through array and if condition met, add relevant
// background color.
for ( i = 0; i < lastColumn - 1; i++){
for ( j = 0 ; j < lastRow - 1; j++){
if(rangeValues[j][i] != ""){
sheet.getRange(j+1,i+7).setBackground("#cc4125");
};
};
};
};

Answer 1

Try this -
function calculate() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();
var sValues = sheet.getDataRange().getValues();
// E = 5, in array it is 4
// G = 7, in array it is 6
// Loop through array and if condition met, do stuff
sValues.forEach(function(row, i) {
if (row[6] != '') {
row[4] = row[4] - row[6];
row[6] = '';
sheet.getRange(i + 1, 7).setBackground('#cc4125');
}
});
sheet.getDataRange().setValues(sValues);
}

Answer 2

Thank you ra89fi, you gave me 99% of what I needed, here is the end result that worked
function calculate() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();
var sValues = sheet.getDataRange().getValues();
// E = 5, in array it is 4
// G = 7, in array it is 6
// Loop through array and if condition met, do stuff
sValues.forEach(function(row, i) {
if (row[6] != '') {
row[4] = row[4] - row[6];
row[6] = '';
sheet.getRange(i + 1, 5).getCell(1,1).setValue(row[4]);
sheet.getRange(i + 1, 7).getCell(1,1).setValue('');
}
});
}