Function to check for duplicates based on condition - google-sheets

Question

I have a simple Google sheet that records what sessions people are signed up for (3 concurrent sessions per day):
The same person cannot be in more than 1 session on a given day. I'd like to create a function in column B that checks for that situation and flags it, as in Susan, Keith, and Amy in the example above (I've highlighted in yellow the conditions that would trigger a flag).
If there were just one date, I'd use a countif (or maybe countifs?) to check for more than 1 TRUE for that date. But with multiple dates, I think some sort of iterative function or query is needed. I have a feeling I may be missing a simple formula, but it's eluding me. I may add more dates, so the solution needs to allow for n number of dates in the range.
UPDATE: My scenario has become a little more complex. I'm designating a potential role each person can play in each session and then using the checkboxes to indicate who is playing what role in each session. A given person can't be in more than 1 session per day (but a given person may be in 0 sessions on a given day). The below image shows this updated scenario, with the yellow highlights showing the conditions that I want flagged via the function in column B.
Here's a link to the Google sheet if you want to create a copy.

Answer 1

Given the use case provided, you can apply the formula below to B3 and drag the auto-complete handle:
=IF(ARRAYFORMULA(SUM(INT(C3:K3))) = COUNTUNIQUE($C$1:$1), "", "FLAG")
I'm converting the Boolean values to INT and summing them up. If the sum is equal to the count of unique days in the first row, then everything is fine, otherwise, FLAG!
In other words, if there are more (or less) checks than days, it should be flagged.
You can also set up a conditional formatting to paint the cell accordingly.
Alternatively, if you’d like to treat each scenario you can use =IFS() as below:
=IFS(ARRAYFORMULA(SUM(INT(C3:K3))) > COUNTUNIQUE($C$1:$1), "HIGHER", ARRAYFORMULA(SUM(INT(C3:K3))) < COUNTUNIQUE($C$1:$1), "LOWER", ARRAYFORMULA(SUM(INT(C3:K3))) = COUNTUNIQUE($C$1:$1), "OK")
References:
Sheets Functions documentation
IF
IFS
ARRAYFORMULA
SUM
INT
COUNTUNIQUE
EDIT:
Since the changes in the original scope significantly impacted my previous answer, here is a suggestion using a custom formula:
function checkFlags(){
var ss = SpreadsheetApp.getActive(); // get active Sheets
var ws = ss.getSheetByName("Sheet1"); // getting tab named "Sheet1"
var currentCellRange = ss.getActiveRange(); // getting active cell, in the context of a custom formula, it gets the one being calculated at the time
var rowIndex = currentCellRange.getRowIndex(); //getting current row number
var rowValues = ws.getRange(`${rowIndex}:${rowIndex}`).getValues()[0]; //getting row cells values
var sessionsList = []; //temp variable to store useful data from cells
for (var i = 0; i < rowValues.length; i++) { //reading cells on the row to create a date/flag array
var cell = rowValues[i]; //getting Range of current cell
if (typeof(cell) == 'boolean'){ //if the current cell has a boolean value, it is a session flag
var headerDate = ws.getRange(2, (i+2)).getDisplayValue(); //getting the header value on row 2 (current date for the session flag)
sessionsList.push({date: headerDate, session: cell});//storing date and session flag value on the temp variable
}
};
var groupBy = function(xs, key) { //handle function to proccess the sessionsList variable and group flag values by 'date'
return xs.reduce(function(rv, x) {
(rv[x[key]] = rv[x[key]] || []).push(x);
return rv;
}, {});
};
var tempGroupedArray = groupBy(sessionsList, 'date'); //grouping temp sessionsList by 'date'. This will return an array like [ { date: '<date>', session: true/false }, { date: '<date>', session: true/false }, ...]
for (dateFlags of Object.entries(tempGroupedArray)) {//looping through the `grouped by date` array
var tempCount = dateFlags[1].filter(x => x.session==true).length; //how many `trues` are for this date
if (tempCount > 1){ //if there is more than one session set as "true" for this date...
return 'FLAG'; //...immediately stop execution and return FLAG
}
};
//if it passed the loop above, it means there is no flags
return ''; //then return blank
}
NOTES: This custom formula will not update the result in the cell after a change on the flag values, you must delete/paste it to force if wanted.