I have written a custom function for Google Sheets in Apps Script. The goal is to have a sheet which automatically calculates who owes how much money to whom (e.g. to split a bill).
My sheet looks like this:
The first bill (Restaurant) is to be split among all 5 and the second bill is to be split among all 5 except Peter, because there is no 0 in B3.
The input for my Apps Script function will be cells B1 to F3 (thus, values AND names). The function works fine - it calculates the correct results. I open that spreadsheet via browser (sheets.google.com) AND via my phone app (Google Sheets). However, on my phone it often happens that the result cell (with the formula =calc_debt(B1:F3)) only displays "Loading ...". What's the problem?
For the sake of completeness, here is custom function's code:
function calc_debt(input) {
var credit = [0, 0, 0, 0, 0]; // credit[0] = Peter, credit[1] = Mark ...
for (var i = 1; i < input.length; i++) { // starting at i = 1 to skip the first row, which is the names!
// first: calculate how much everybody has to pay
var sum = 0;
var people = 0;
for (var j = 0; j <= 4; j++) {
if (input[i][j] !== "") {
sum += input[i][j];
people += 1;
}
}
var avg_payment = sum / people;
// second: calculate who has payed too much or too little
for (var j = 0; j <= 4; j++) {
if (input[i][j] !== "") {
credit[j] += input[i][j] - avg_payment;
}
}
}
// this function is needed later
function test_zero (value) {
return value < 0.00001;
};
var res = ""; // this variable will contain the result string, something like "Peter to Mark: 13,8 | Katy to ..."
while (!credit.every(test_zero)) {
var lowest = credit.indexOf(Math.min.apply(null, credit)); // find the person with the lowest credit balance (will be minus!)
var highest = credit.indexOf(Math.max.apply(null, credit)); // find the person with the highest credit balance (will be plus!)
var exchange = Math.min(Math.abs(credit[lowest]), Math.abs(credit[highest])); // find out by how much we can equalize these two against each other
credit[lowest] += exchange;
credit[highest] -= exchange;
res += input[0][lowest] + " to " + input[0][highest] + ": " + exchange.toFixed(2) + " | "; // input[0] = the row with the names.
}
return res;
}