First cell in active row during script execution - google-apps-script

Question

I am using the code below to view through a sheet, and change the first cell background to red if any other cells are red. What I would like, is to change the first cell in each row to red, only if that row contains a red cell. This code works through the spreadsheet, but only makes cell A1 red. How do I get it to affect the first cell of each row independently?
function MakeRed(){
var book = SpreadsheetApp.getActiveSpreadsheet();
var sheet = book.getActiveSheet();
var first_column = "B";
var first_row = 1;
var last_row = sheet.getLastRow();
var last_column = sheet.getLastColumn();
var active_row = 1;
var range_input = sheet.getRange(1,1,last_row,last_column);
var range_output = sheet.getRange("A1");
var cell_colors = range_input.getBackgroundColors();
var color = "#ff0000";
var count = 0;
for(var r = 0; r < cell_colors.length; r++) {
for(var c = 0; c < cell_colors[0].length; c++) {
if(cell_colors[r][c] == color) {
count++;
range_output.setBackground("#ff0000");
} else {
count--;
if (count == 0) {
range_output.setBackground("#ffffff");
}
}
}
}
}

Answer 1

I would suggest you do the whole stuff in the array of background colors you already have instead of calling a spreadsheet service each time the condition is true.
Code becomes simpler because I used the indexOf array method in the condition
function MakeRed(){
var book = SpreadsheetApp.getActiveSpreadsheet();
var sheet = book.getActiveSheet();
var first_column = "B";
var first_row = 1;
var last_row = sheet.getLastRow();
var last_column = sheet.getLastColumn();
var active_row = 1;
var range_input = sheet.getRange(1,1,last_row,last_column);
var range_output = sheet.getRange("A1");
var cell_colors = range_input.getBackgroundColors();
var color = "#ff0000";
var count = 0;
for(var r = 0; r < cell_colors.length; r++) {
Logger.log(cell_colors[r].indexOf(color));// just to check, you can remove this of course ...
if(cell_colors[r].indexOf(color)>-1) {
count++;
cell_colors[r][0]=color;
} else {
count--;
if (count == 0) {
cell_colors[r][0]="#ffffff";
}
}
}
range_input.setBackgroundColors(cell_colors);// update sheet colors
}
EDIT : I don't really understand the idea behind the "count" thing... it works the same way without it (code below) :
function MakeRed(){
var book = SpreadsheetApp.getActiveSpreadsheet();
var sheet = book.getActiveSheet();
var first_column = "B";
var first_row = 1;
var last_row = sheet.getLastRow();
var last_column = sheet.getLastColumn();
var active_row = 1;
var range_input = sheet.getRange(1,1,last_row,last_column);
var range_output = sheet.getRange("A1");
var cell_colors = range_input.getBackgroundColors();
var color = "#ff0000";
for(var r = 0; r < cell_colors.length; r++) {
Logger.log(cell_colors[r].indexOf(color))
if(cell_colors[r].indexOf(color)>-1) {
cell_colors[r][0]=color;
} else {
cell_colors[r][0]="#ffffff";
}
}
range_input.setBackgroundColors(cell_colors);// update sheet colors
}
edit 2 : this version will reset col A to white if no other red cell is in the row
function MakeRed(){
var book = SpreadsheetApp.getActiveSpreadsheet();
var sheet = book.getActiveSheet();
var first_column = "B";
var first_row = 1;
var last_row = sheet.getLastRow();
var last_column = sheet.getLastColumn();
var active_row = 1;
var range_input = sheet.getRange(1,1,last_row,last_column);
var range_output = sheet.getRange("A1");
var cell_colors = range_input.getBackgroundColors();
var color = "#ff0000";
for(var r = 0; r < cell_colors.length; r++) {
var rowWoColA = cell_colors[r].slice(1);
if(rowWoColA.indexOf(color)>-1) {
cell_colors[r][0]=color;
} else {
cell_colors[r][0]="#ffffff";
}
}
range_input.setBackgroundColors(cell_colors);// update sheet colors
}

Answer 2

Change var range_output = sheet.getRange("A1"); to the range you want edit.
You could do this in the loop:
for(var r = 0; r < cell_colors.length; r++) {
for(var c = 0; c < cell_colors[0].length; c++) {
if(cell_colors[r][c] == color) {
count++;
// Assuming you only want to change bg color of the first column on each row
sheet.getRange(r,1).setBackground("#ff0000");
} else {
count--;
if (count == 0) {
sheet.getRange(r,1).setBackground("#ffffff");
}
}
}
}