getDisplayValues is not returning a 2-D array - arrays

Question

I am writing a script that updates a cell in a Google Sheet based on the intersection of a Row and Column. I find the row by iterating through a list of unique teacher names. When I find the name, I capture its row number in the variable "row". I then iterate through a range of column headers that are dates to find the specific date, and capture its column number as the variable "column". However, when I look at the structure of each object in my code, the "names" object appears as [[Person1], [Person2],..., [PersonX]] whereas the "dates" object appears as [[date1, date2,..., dateX]]. I can iterate through the names object just fine, but the dates object, not so much, and I suspect it is due to the structure.
I understand that the getDisplayValues returns a string and it works fine in another area of my code when I need to grab the date from a cell and name it "dateValue". But when I look for that dateValue in the "dates" object in the code below, that is where my code fails.
Here is a sample of the code:
function updateTracker(){
var sheet = SpreadsheetApp.getActiveSpreadsheet();
var teacherName = sheet.getRange('F7').getDisplayValue();
var dateValue = sheet.getRange('N7').getDisplayValue();
var tracker = SpreadsheetApp.openById('AAAbbbCCCxxxYYYzzz111222333');
var tab = tracker.getSheetByName('Tracker');
var names = tab.getRange(1, 4, tab.getLastRow(), 1).getDisplayValues();
var dates = tab.getRange(1, 1, 1, tab.getLastColumn()).getDisplayValues();
for (var i in names) {
if (names[i][0] === teacherName) {
var row = parseInt(i+1);
}
}
for (var j in dates){
if (dates[0][j] === dateValue) {
var column = parseInt(j+1);
}
}
var cell = tab.getRange(row, column).setValue('x');
}
I get an error on that last line that getRange expects (number, number) but it getting (number, null).
Any suggestions on editing the code?

Answer 1

Logic:
In case of [[Person1], [Person2],..., [PersonX]], You iterate the "outer" array. There are X elements in the outer array. Each element itself is a array("inner") like [Person1] with only 1 primitive element each lime Person1.
Whereas the "dates" object appears as [[date1, date2,..., dateX]]. There is only 1 element in the outer array[date1, date2,..., dateX] and this array contains many elements like date1.
Solution:
You should iterate the inner array in the dates array:
for (var j in dates[0]){//note `[0]`
Using for...in to iterate arrays is also considered bad practice. Use for...of instead:
let column = null, j = 0;
for (const date of dates[0]){
j++;
if (date === dateValue) {
column = parseInt(j+1);//also bad to declare var in a block. Moved declaration outside
}
}
References:
What does the range method getValues() return and setValues() accept?
Why is using "for...in" for array iteration a bad idea?
for...of -MDN reference