Indirect Addresses in Array Formula - google-sheets

Question

I have the following formula
=average(arrayformula(indirect(split(A1,","))))
Where A1 contains a list of cell addresses, such as E4,E6,E12. I expect this to be equivalent to =AVERAGE(E4,E6,E12), but this does not behave as expected, yielding 4 no matter what the data in the cells are. Preliminary research indicates that the INDIRECT() function doesn't pass through ARRAYFORMULA() correctly. Attempting SUM() on the outside yields precisely the same results.
Any ideas on how to average the values of cells obtained indirectly by a list of cell addresses?
I do have a list of columns and the row doesn't ever change for this average calculation, so I'm wondering if I could do some kind of subset instead, such as
=AVERAGE(RANGE){LIST_TO_SUBSET_BY}

Answer 1

I'm not sure about a built-in formula to do this so I've written a custom function to do it for you.
Go to Tools -> Script editor and replace the existing function with the code below and then save the project.
Now in your spreadsheet in any cell =CUSTOMFUNCTION(A1) where A1 contains a list of comma-separated cell references.
NOTE:
Updating values in the referenced cells won't force a recalculation of this formula, only updating cell A1 will.
I suggest you also go to File -> Spreadsheet settings -> Calculation and change 'Recalculation' to 'On change and every minute' that will force a recalculation of this function every minute.
/**
* Returns the average value of a dataset.
* #param {"A1"} cell The cell containing the list of cell references.
* #return The input repeated a specified nunmber of times.
* #customfunction
*/
function CUSTOMAVERAGE(cell){
var ss = SpreadsheetApp.getActiveSheet();
var array = [];
var cellRefs = cell.split(",");
for(var i in cellRefs){
array.push(ss.getRange(cellRefs[i]).getValue());
}
var sum = 0;
for(var i in array){
sum += array[i]
}
var avg = sum/array.length;
return avg;
}

Answer 2

Though this is a very specific application in response to this question, for the sake of the knowledge base, I'd like to show how this can be done without a script.
To give this context, imagine the LIST_CELL is a list of question numbers
(which are entered in as a header row, call the range QUESTIONS) on a test that correspond to certain standards, and the goal is to average only the questions that correspond to the standard next to which the list is written, and for each student. Using
=iferror(join(",",ArrayFormula(match(split(LIST_CELL,","),QUESTIONS,FALSE))),"")
The split function splits the a hand-entered list of questions on commas, the match function returns the column number of that particular question in QUESTIONS, and the join function joins the data back together. ArrayFormula allows the match to be performed on an array instead of just the first value.
Another single row heading lists the standards to which each question has been matched (possibly to more than one standard) by the comma separated list in LIST_CELL. For a column list of students in A:A, each standard needs to average the scores of every question that is listed next to the standard. This is accomplished by the nifty (if clunky):
average(ArrayFormula(hlookup(split(vlookup(LOOKUP_VAL,SEARCH_RANGE,COL_W_LIST),","),DATA_SOURCE,row(CURRENT_CELL))))
Breakdown from center outward:
LOOKUP_VAL is the value being looked up (the one that has multiple matches); in the example context, it's the standard.
SEARCH_RANGE is a range of cells containing both the list of lookup value (the standards in context) and the comma separated lists of column numbers generated by the first function. COL_W_LIST is the column number in the array SEARCH_RANGE that contains the list of row numbers matched from LIST_CELL.
Split takes the elements apart and placed them in a temporary array so that hlookup can be performed on each element. Via ArrayFormula the hlookup grabs each value on the same row in the appropriate QUESTIONS column - in context, it grabs the point scores for each question matched to the standard.
Finally, average is self-explanatory, and does take an array as input apparently.
These two functions in combination allow of use of indirect cell references in an array formula, and solves the much asked, "how do I include multiple matches in a calculation" question. At least in this specific context.
EDIT
There is an example "template" with this implemented here. You'll need to make your own copy to edit it.