SUMCOLS and SUMROWS functions for Dynamic Arrays
Create new functions that SUM each column in a dynamic array (SUMCOLS(Ref#)) to produce a row of totals, and SUM each row to produce a column of totals (SUMROWS(Ref#))
Also COUNTCOLS, COUNTROWS, AVERAGECOLS, AVERAGEROWS, but these are less important than SUMCOLS & SUMROWS.
8 comments

Charles Williams commented
@Kevin,
Would be nice to address your DA Table problem, but that would not solve the problem for general DA totals.

Kevin Osborn commented
I understand where you are going with this but I'm not going to vote it up. IMO a better solution is to allow 1 dynamic array function inside a table. Not only will this address your issue with sum/count/avg for columns because tables can have a "total" row but it will also fix the deficiency in dynamic arrays whereby structured/table reference cannot be used to reference a column in a dynamic array so the developer is forced to revert back to column numbers. Similarly instead of having sum, count, average rows I'd rather see a "Row Total" added to tables (similar to column totals).

Peter Bartholomew commented
Hi Charles
I fully support this initiative. I had posted a related idea but I am not too fussed about the implementation provided the functionality is there.
My aim is not simply to use DA here and there but to build dynamic solutions from the ground up using nothing but dynamic arrays. At the moment my solutions are full of matrix multiplication (MMULT) to perform aggregations by row and by column and to accumulate arrays in either direction.
There is no chance of rolling such methods out across the Excel community, so a suite of new functions is essential to the success of DA.
It is such a relief to move away from manual knifeandfork selection of cells and rows for calculation (more accurately selection by mouse and keyboard shortcuts) and let the calculation logic speak for itself based upon references to entire arrays and tables.

Jon Acampora commented
Great idea!

Roger Govier commented
Excellent idea Charles and I have tested your own functions that you have already written which work perfectly.
However, I think it would be even more useful if there was a way to pass an optional array to the function to excluded certain columns otherwise you end up summing dates and unit prices etc., which is neither use to man nor beast.
e.g. =SUMCOLS(E7#,{1:6,9}) which would exclude summing the first 6 columns and the 9th for example. 
BetterSolutions.com commented
Great Suggestion

Jeff commented
Definitely needed! MMULT is not intuitive or easy for the average user

Wyn Hopkins commented
Essential to really take full advantage of Dynamic Arrays