Replacing repeating (following) values of a list by a single value

[pnapiera]

Hi,

On of the column in my table consists of lists. I am looking for a solution to convert the lists in a way that repeating values that follow one after another are replaced by single value.

Ex.

[A,A,A,B,B,C,C,B,B,B,C,C,C,A] => [A,B,C,B,C,A]

[C,C,B,B,A,A,C,C,B,A,A,B] = > [C,B,A,C,B,A,B]

Could you please share your suggestions?

[Anonymous · Accepted solution]

Hi @pnapiera 

Your example looks more like records :). If they are actually lists.

You can use this:

let
    Source = {"A","A","A","B","B", "C","C","B","B","C","C","C","A"},
    ToTable = Table.FromColumns({Source}),
    Distill = Table.Group(ToTable, {"Column1"}, {}, GroupKind.Local)[Column1]
in
   Distill

or this:

let
    Source = {"A","A","A","B","B", "C","C","B","B","C","C","C","A"},
    Distill = List.Accumulate(Source, {}, (s,a) =>  if a = List.Last(s) then s else s & {a})
in
    Distill

Kind regards,

JB

[v-juanli-msft · Accepted solution]

Hi @pnapiera 

jborro's solution is great if you have one column in table.

If you have example data as below, you could modify jborro's method as below to make it work.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlSK1YlWMgKTxkqxsQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [index = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"index", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "list", each {"A","A","A","B","B", "C","C","B","B","C","C","C","A"}),
    Custom1 = Table.ReplaceValue(#"Added Custom",each [list],each Function.Invoke((_list as list)=> List.Accumulate(_list, {}, (s,a) =>  if a = List.Last(s) then s else s & {a}),{[list]}),Replacer.ReplaceValue,{"list"}),
    #"Expanded list" = Table.ExpandListColumn(Custom1, "list")
in
    #"Expanded list"

Best Regards
Maggie
Community Support Team _ Maggie Li
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[pnapiera]

Thank you very much @Anonymous and @v-juanli-msft .

Both answers are helpful and this is exactly what I needed. Moreover I learned about the power of List.Accumulate.

[Anonymous · Accepted solution]

Hi @pnapiera 

Your example looks more like records :). If they are actually lists.

You can use this:

let
    Source = {"A","A","A","B","B", "C","C","B","B","C","C","C","A"},
    ToTable = Table.FromColumns({Source}),
    Distill = Table.Group(ToTable, {"Column1"}, {}, GroupKind.Local)[Column1]
in
   Distill

or this:

let
    Source = {"A","A","A","B","B", "C","C","B","B","C","C","C","A"},
    Distill = List.Accumulate(Source, {}, (s,a) =>  if a = List.Last(s) then s else s & {a})
in
    Distill

Kind regards,

JB