Question on converting array into sub-arrays

To achieve the grid you want, you will be looking for arrays in this format instead, so each can be used as a column: {a,d,g},{b,e,h},{c,f,i}. This function below will handle a dynamic sized list and column count and perform a type of pivoting for you, returning an array of arrays in the desired format which you should be able to iterate through and generate your columns, give it a try:

rule!chris_pivot()

with(
local!array: {"a","b","c","d","e","f","g","h","i"},
local!columns: 3,
local!count: count(local!array),
local!indexes: apply(rule!chris_pivotGetIndex(separation: local!columns, num: _, count: _),
merge(
1+enumerate(local!columns),
apply(rule!chris_pivotGetSizes(max: local!count, size: local!columns, start: _), 1+enumerate(local!columns))
)
),
local!newArrays: apply(rule!chris_pivotGetItems(array: local!array, indexes: _),local!indexes),

local!newArrays
)

Helper Rules:

rule!chris_pivotGetIndex(num, separation, count) - inputs single valued integers:

joinarray(
apply(rule!chris_pivotGetIndex_helper(num: ri!num, separation: ri!separation, index: _), enumerate(ri!count))
,","
)

rule!chris_pivotGetIndex_helper(num, separation, count) - inputs single valued integers:

(ri!index * ri!separation) + ri!num

rule!chris_pivotGetSizes(max, start, size) - inputs single valued integers:

ceiling((ri!max+1-ri!start)/ri!size)

rule!chris_pivotGetItems(array,index) - both inputs text, 'array' is multiple:

index(ri!array,apply(fn!tointeger,split(ri!indexes,",")),null)

To achieve the grid you want, you will be looking for arrays in this format instead, so each can be used as a column: {a,d,g},{b,e,h},{c,f,i}. This function below will handle a dynamic sized list and column count and perform a type of pivoting for you, returning an array of arrays in the desired format which you should be able to iterate through and generate your columns, give it a try:

rule!chris_pivot()

with(
local!array: {"a","b","c","d","e","f","g","h","i"},
local!columns: 3,
local!count: count(local!array),
local!indexes: apply(rule!chris_pivotGetIndex(separation: local!columns, num: _, count: _),
merge(
1+enumerate(local!columns),
apply(rule!chris_pivotGetSizes(max: local!count, size: local!columns, start: _), 1+enumerate(local!columns))
)
),
local!newArrays: apply(rule!chris_pivotGetItems(array: local!array, indexes: _),local!indexes),

local!newArrays
)

Helper Rules:

rule!chris_pivotGetIndex(num, separation, count) - inputs single valued integers:

joinarray(
apply(rule!chris_pivotGetIndex_helper(num: ri!num, separation: ri!separation, index: _), enumerate(ri!count))
,","
)

rule!chris_pivotGetIndex_helper(num, separation, count) - inputs single valued integers:

(ri!index * ri!separation) + ri!num

rule!chris_pivotGetSizes(max, start, size) - inputs single valued integers:

ceiling((ri!max+1-ri!start)/ri!size)

rule!chris_pivotGetItems(array,index) - both inputs text, 'array' is multiple:

index(ri!array,apply(fn!tointeger,split(ri!indexes,",")),null)