List.Generate, make behave like Accumulate or XL REDUCE

[Dicken]

Hi,
my staring point was this, i wanted to accumute fieds to a  record;  so i used; 

let
  f    = {List.Sum, List.Max, List.Average},
      head = {"sum", "max", "avg"},
      pos  = {0, 1, 2},
      val  = {2, 3, 1, 5, 2, 1}
    in
      List.Accumulate(pos, [], (s, c) => Record.AddField(s, head{c}, Function.Invoke(f{c}, {val})))

so simplifying you can have;

= let val = {12,21,34} , pos = {0,1,2}, 
head = {"a","b","c"}  
in List.Accumulate(  pos, [], (s,c)=> Record.AddField( s, head {c} , val {c} )) 

i have been trying to replaicate using generate; i have;  but this accumutes a  list of records, with the final being 
what is wnated.  is there a way to just generate each field , 

 let 
head = { "sum", "max", "avg"}, 
val = {2,3,1,5,2,1}
 in
  List.Generate(()=> [ x = 0, y = Record.AddField( [],head {0}, val{0} ) ],
                 each [x] < List.Count( head), 
                 each [x = [x] + 1, y = Record.AddField( [y], head {x} , val {x} ) ], 
each [y] )

i don't know if this is possible using Gen,  perhaps putting it insided a record [  x = y, z = Listgenerate ] ? 
any suggestions ? or as i think perhaps not doable ? 
just to note, if anyone dashes of a quick repsonse i may not be able to respond until tomorrow. 
Richard

[ronrsnfld]

You can use List.Generate, but it seems cumbersome when what you want to do is accumulate results into a single record as List.Accumulate can do. List.Generate returns a List by design.

One method would be to wrap List.Generate inside List.Last

let 
  val = {12,21,34} , 
  pos = {0,1,2}, 
  head = {"a","b","c"},
 
  res =  List.Last(List.Generate(
    ()=>[idx=0, x=Record.AddField([],head{idx},val{idx})],
    each [idx] < List.Count(head),
    each [idx=[idx]+1, x=Record.AddField([x],head{idx},val{idx})],
    each Record.Combine({[x]})))
in
    res

Another method would be to return a List of Records and then combine them into a single record:

let 
  val = {12,21,34} , 
  pos = {0,1,2}, 
  head = {"a","b","c"},
 
  res = Record.Combine(List.Generate(
    ()=>[idx=0, x=Record.AddField([],head{idx},val{idx})],
    each [idx] < List.Count(head),
    each [idx=[idx]+1, x=Record.AddField([],head{idx},val{idx})],
    each [x]))
in
    res

Please note that the most efficient method (within your constraints) would be by using List.Accumulate. Theoretically, Record.Combine(List.Generate(...  should be more efficient than List.Last(List.Generate(... as one is only generating a single record for each "loop" in the former, and increasing numbers of records in the latter.

[Ahmedx · Accepted solution]

and try this

let 
f    = {List.Sum,List.Max, List.Average},
head = { "sum", "max", "avg"}, 
val = {2,3,1,5,2,1},
to=
  List.Generate(()=> [ i = 0, j = Record.AddField( [],head {i}, f{i}(val) )  ],
                 (x)=> x[i] <= List.Count( head)-1, 
                 (x)=> [i = x[i] + 1, j = Record.AddField( [],head {i},f{i}(val))
],
                 (x)=>x[j])
in
  Record.Combine( to)

[Dicken]

Thanks, will work through properly,  i like anythiing that invvolvves records 😊

[Ahmedx]

let
    f = {List.Sum, List.Max, List.Average},
    head = {"sum", "max", "avg"},
    val = {2, 3, 1, 5, 2, 1},
    to = List.Generate(
        () => 0, 
        (x) => x <= List.Count(f) - 1, 
        (x) => x + 1, 
        (x) => Record.FromList({f{x}(val)}, {head{x}})
    )
in
    Record.Combine(to)
============================
let
    f = {List.Sum, List.Max, List.Average},
    head = {"sum", "max", "avg"},
    val = {2, 3, 1, 5, 2, 1},
    
    to = List.Generate(
        () => 0, 
        (x) => x <= List.Count(f)-1, 
        (x) => x + 1,
        (x) =>  Record.AddField([],head {x}, f{x}(val) ))
in
    Record.Combine(to)

[Ahmedx]

To get such a result, you need to use neither List.Accumulate nor List.Generate

let
  f    = (x)=> {List.Sum(x), List.Max(x), List.Average(x)},
      head = {"sum", "max", "avg"},
      val  = {2, 3, 1, 5, 2, 1},
   to =     Record.FromList(f(val), head)
    in to

[Dicken]

yes, i know , but i wanted to use LIst.Generate,  can it be done ? 

[Ahmedx]

pls try

let
    f  = {List.Sum, List.Max, List.Average},
      head = {"sum", "max", "avg"},
      n = List.Count(head)-1,
      val  = {2, 3, 1, 5, 2, 1},
     to =  List.Generate(()=>[i=0, j=f{i}],
               (x)=> x[i]<=n,
               (x)=>[i= x[i]+1,j =f{i}],
               (x)=> Function.Invoke(x[j],{val}))
in
   Record.FromList(to,head)

[lbendlin]

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[Dicken]

As far as i can tell there is no way to upload a copy of the file created, if there is could you plase let me know.