List.Unzip wanted

[Anonymous]

let suppose we have two lists for which I want to keep the correspondence in the order of the elements.
So if I change the order of the first one of the lists, the elements of the second list also arrange themselves in corresponding positions.
This is easily done using the List.Zip function.

But to get back two separate lists  you need a sort of List.Unzip function.

I imagined one based on the use of List.accumulate

How else can you do the reverse operation of List.Zip?

[Smauro]

Well,

Now I've made a tweaked List.Zip:

(ListGiven as list) as list =>
    let
        n =
            List.Max(
                List.Transform(
                    ListGiven,
                    each try List.Count(_) otherwise 1
                )
            ),
        GetK =
            (k) =>
                List.RemoveFirstN(
                    List.RemoveLastN(
                        List.Transform(
                            ListGiven,
                            each try _{k} otherwise null
                        ),
                        each _ = null
                    ),
                    each _ = null
                ),
        Zip =
            List.Generate(
                () =>
                    [
                        l =
                            List.RemoveFirstN(
                                List.RemoveLastN(
                                    List.Transform(
                                        ListGiven,
                                        each try _{0} otherwise _
                                    ),
                                    each _ = null
                                ),
                                each _ = null
                            ),
                        k = 1
                    ],
                each [k] <= n,
                each
                    [
                        l = GetK([k]),
                        k = [k] + 1
                    ],
                each [l]
            )
    in
        Zip

Contrary to List.Zip, it will also take single values, and cut leading and trailing nulls.

If you want to test it, you could name it fnListZip and use this:

let
    l = {1,3,5,7,9},
    k = {2,4,6},
    #"ListZip(l)" = List.Zip({l}),
    #"fnListZip(l)" = fnListZip({l}),
    #"ListZip(k,l)" = List.Zip({k,l}),
    #"fnListZip(k,l)" = fnListZip({k, l}),
    #"ListZip(ListZip(k,l))" = List.Zip(#"ListZip(k,l)"),
    #"fnListZip(fnListZip(k,l))" = fnListZip(#"fnListZip(k,l)"),
    #"ListZip(l,k,l)" = List.Zip({l, k, l}),
    #"fnListZip(l,k,l)" = fnListZip({l, k, l}),
    #"ListZip(ListZip(l,k,l))" = List.Zip(#"ListZip(l,k,l)"),
    #"fnListZip(fnListZip(l,k,l))" = fnListZip(#"fnListZip(l,k,l)"),
    NotReallyAListZip = {{1,2},{3,4},{5,6},7,9},
    #"ListZip(NotReallyAListZip)" = List.Zip(NotReallyAListZip),
    #"fnListZip(NotReallyAListZip)" = fnListZip(NotReallyAListZip),
    NotReallyAListZipB = {1,2,3,4,{5,"Here Is Something"},7,9},
    #"ListZip(NotReallyAListZipB)" = List.Zip(NotReallyAListZipB),
    #"fnListZip(NotReallyAListZipB)" = fnListZip(NotReallyAListZipB)
in
    #"fnListZip(NotReallyAListZipB)"

Best,

Spyros

[Smauro]

Hey @Anonymous ,

I came up with this:

(ListGiven as list) as list =>
    let
        n = List.Count(ListGiven{0}),
        Acc =
            (ListGiven, k, n) =>
                let
                    ListK =
                        if k < n then
                            List.Transform(ListGiven, each _{k})
                        else
                            {},
                    NewList =
                        if k < n then
                            ListK & @Acc(ListGiven, k + 1, n)
                        else
                            ListK
                in
                    NewList,
        UnZipped = Acc(ListGiven, 0, n)
    in
        UnZipped

@Mariusz' answer is better and certainly easier. What I came up with just gives one list.

[Mariusz · Accepted solution]

Hi @Anonymous 

You can zip it again, this will reverse the zip, or am I missing something?

= List.Zip( List.Zip( { { 1, 2 }, { 3, 4 }, { 5, 6 } } ) )

Best Regards,
Mariusz

If this post helps, then please consider Accepting it as the solution.

Please feel free to connect with me.
LinkedIn

[Anonymous]

wow. this is the solution :-).

I was speculating on the InsertRanges

insertRanges 

function and I was thinking about situations of possible errors to manage.
In particular, I was thinking of cases where the different length of the vectors involved can lead to error.
Aside from these cases, a potential error situation occurred to me which also depends on the order of the elements in the vectors.
And on this I looked for ways to manage the situation.

la situazione si potrebbe presentare quando positions and ranges are, for instance,

{1, 5, 2} and  {22,55, {33,44}}.

I tryed to solve in the following way:

let
    Source = List.Sort(List.Zip({{1, 5, 2}, {22,55, {33,44}}}),each _{0})
in
    List.Accumulate(Source, {{},{}},(s,c)=>{s{0}&{c{0}},s{1}&{c{1}}})

But now there is not needs of news unzip function.

[Anonymous]

...

in some respects the transformation carried out by the list.zip function on a set of lists is analogous (isomorphic?!) to that made by the table.transpose function on the set of columns of a table.
therefore like the transpose (transpose (T)) = T, should be also List.Zip (list.Zip (lists)) = lists

this property indicates yet another way of realizing the list.zip function through other functions

let
    ListZipUnZip = (lsts) =>  Table.ToColumns(Table.Transpose(Table.FromColumns(lsts)))
in
    ListZipUnZip

of course also the dual situation is valid.

if you wanted, for very personal reasons, to simulate the Table.Transpose function, you could use List.Zip

let
    transpose = (tab) =>  Table.FromColumns(List.Zip(Table.ToColumns(tab)))
in
    transpose