Forum Discussion
Fill BLANKs down, up or both in column(s) - similar to Power Query
My variant:
Filler =LAMBDA(table,LET( header, TAKE(table, 1), data, DROP(table, 1), counter, SEQUENCE(COLUMNS(data)), FillDown, LAMBDA(a, v, IF(v = "", a, v)), Complete, LAMBDA(vector, LET(ini, TAKE(TOCOL(vector, 1), 1), SCAN(ini, vector, FillDown))), Stack, DROP(REDUCE("", counter, LAMBDA(a, v, HSTACK(a, Complete(INDEX(data, , v))))), , 1), VSTACK(header, Stack) ))
Still need to fully understand how this works but this seems very straightfoward 🙂
The core functionality of BYCOLλ is also intended to be widely deployable. The assumption is that some function FNλ needs to be applied to every column of an array (or range). Rather than rewriting the function FNλ to address multiple columns, BYCOLλ splits to problem into two parts and solves each half independently. Recursion means that eventually one reaches the point where the argument is a single column and FNλ may be applied directly to give a single result.
Whereas the built-in BYCOL function will only return the result if each application of the function returns a scalar value, BYCOLλ uses HSTACK to build an array of arrays.
A problem with the alternative approach of using REDUCE and HSTACK to build an array of array is that the early results may be copied 10,000s of times during the stacking steps. This gets to be expensive in terms of computing resource. The bisection approach limits the steps of copying any given result to form build bigger datasets to 14 at the most.
I hope that by describing the intent of the 'home-knitted' helper function, I will simplify life for anyone planning to reverse engineer it from the code.