google sheets custom averaging function - google-apps-script

Question

I have basic coding skills from college but not familiar with Apps Script for Google Sheets so I'm sure my code is all over the place and there is probably an easier way but I REALLY need some help before I pull all my hair out.
What I'm trying to do:
create a function that returns the TOTAL average of a strain, from a column of averages with all strains on the sourceSheet (has multiple rows of same strain) and put into coordinating row (1 row per strain) on strainSheet. The part I get lost at is trying to make the function keep adding the averages to get a total average when there are multiple lines of the same strain.
Here's the code I have:
function getAvgYield(x) {
//Average Strain Yield function
var strainName1 = x;
//Make Spreadsheets
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sourceSheet = ss.getSheetByName('Strain Yields');
//var strainSheet = ss.getSheetByName('Strains');
//get row number of strainName2 being used
var sourceCell = sourceSheet.getCurrentCell().getRow();
//input necessary data from source sheet
var strainName2 = sourceSheet.getRange(sourceCell, 1).getValue();
var avgPerPlant = sourceSheet.getRange(sourceCell, 5).getValue();
//create & define variables
var avgs = 0;
var avgYield = 0;
var tempYield = 0;
if (strainName1 == strainName2)
{
tempYield += avgPerPlant;
avgs++;
sourceCell++;
strainName2 = sourceSheet.getRange(sourceCell, 1).getValue();
} else
{
avgYield = tempYield / avgs;
avgs = 0;
tempYield = 0;
sourceCell++;
return avgYield;
}
avgYield = tempYield / avgs;
avgs = 0;
tempYield = 0;
return avgYield;
}
EDIT:
Here are screengrabs of the sheets. The info in "strain Yields" is being pulled from another document.
trying to fill "average yield" column
.
from the average yield column in this sheet - but adding same strains together.
.
hope this helps

Answer 1

Try this in cell C2 on the Strains tab.
=AVERAGEIF('Strain Yields'!A:A,A2,'Strain Yields'!E:E)
AVERAGEIF()

Answer 2

You could make a script that filled that for you, but it’s actually more flexible to have a function that computes and returns the result, so it can be used in different projects:
/**
* Compute the average for each group
*
* #param criteria_range Column of criterias to check the groups against (will be checked against group).
* #param group_range Column with the names of the group.
* #param average_range Column of values to be averaged if the criteria is matched with the group.
* #param no_elems Message to show if the group has no elements. By the fault it's "No elements".
*
* #returns the average of the values for each group
*/
function AVERAGEGROUPS(criteria_range, group_range, average_range, no_elems="No elements") {
// Input cleanup
criteria_range = criteria_range.map(row => row[0])
group_range = group_range.map(row => row[0])
average_range = average_range.map(row => row[0])
// Calculate all the averages
const nelements = Math.min(criteria_range.length, average_range.length)
return group_range.map(group => {
if (!group) return // early return if it doesn't have a group
let total = 0
let count = 0
for (let i = 0; i < nelements; i++) {
if (criteria_range[i] === group) {
total += average_range[i]
count++
}
}
if (count === 0) {
// Prevent dividing by 0
return no_elems
}
return total / count
})
}
Notice that this algorithm works only for columns. This makes the code way simpler and it’s your use case (and I think the most usual).
To use it, add the following to the “Average Yield” header:
={"Average Yield"; AVERAGEGROUPS('Strain Yields'!A2:A, A2:A, 'Strain Yields'!B2:B)}
Algorithm rundown
The first thing the function does is extract the values from the 2D array of values (array of rows). It does so by getting the first element of the row, so it ends up having a single column of values in an array.
range.map(row => row[0]) // Returns the values in the first column
Now it’s time for the average. nelements is just the length of the elements that we have to check. It’s computed as the minimum of length to prevent the code going out of range. Then we use map (MDN documentation) to make a 1:1 mapping between each group and the average. Inside it’s the actual average computation.
This is quite simple to do, we need to add the elements and the count if it’s part of the group and divide it at the end. We need to be careful of groups without elements. In that case we will return a string stating that (there is no way to return an error).
References
Array.prototype.map() (MDN)
Math.min() (MDN)
Average (Wikipedia)