Add column with list.generate

[Anonymous]

i want to add an index column (b) which is increased by  another column (a) while value is changed.

Like This

A	B
0	1
1	2
0	3
0	3
1	4
0	5

 i found two solutions for this.

First one;

= Table.AddColumn(#"Added Custom", "B", each let index=[Index],custom=[Custom]
in
Table.RowCount(
Table.SelectRows(#"Added Custom",each [Index]<=index and [Custom]=1
)
))

but this makes query too slow.

another one;

= Table.AddColumn(#"Added Custom", "B", each (let Custom=#"Added Custom"[Custom] in
List.Generate( () =>
[CurrentItem = Custom{0}, Index =1 , Counter = 1],
each [Counter] <= List.Count(Custom),
each [
CurrentItem = Custom{[Counter]},
DifferenceToPrevious = CurrentItem - [CurrentItem],
Index = if DifferenceToPrevious >= 1 then [Index] + 1 else [Index],
Counter = [Counter] + 1
],
each [Index]
)))

this query assigned a list instead of a value in every cell.  

Thank you in advance.

[Jimmy801 · Accepted solution]

Hello @Anonymous 

I would suggest you to do this with List.Accumulate. After you created the list that represents your index-column you have to integrate it your current table with Table.ToColumns and Table.FromColumns. Check out this example.

Give it a try and if you have performance issue we can check if we can enhance it a little bit

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlCK1YlWMgSTBkgkXCQWAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [A = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"A", Int64.Type}}),
    CreateNewIndexColumn = List.RemoveFirstN
    (
        List.Accumulate
        (
            #"Changed Type"[A],
            {1},
            (state,current)=> state & {List.Last(state) + current}
        )
    )
,

    AddIndexColumnToTable = Table.FromColumns
    (
        Table.ToColumns(#"Changed Type" ) & {CreateNewIndexColumn},
        Table.ColumnNames(#"Changed Type") & {"Index"}
    )
in
    AddIndexColumnToTable

 Copy paste this code to the advanced editor in a new blank query to see how the solution works.

If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy

[Anonymous]

2MrowsX20cols in 1'30"

let
    Source = List.Transform(List.Random(2000000), each Number.Round(_)),
    #"Converted to Table" = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Muplicated Column" = Table.FromColumns(List.Repeat({#"Converted to Table"[Column1]}, 20)),
   
    #"Grouped Rows" = Table.Group(#"Muplicated Column", {"Column1"}, {{"all",each _}},GroupKind.Local),
    #"Added Index" = Table.AddIndexColumn(#"Grouped Rows", "Index", 1, 1, Int64.Type),
    #"Expanded all" = Table.ExpandTableColumn(#"Added Index", "all", {"Column2", "Column3", "Column4", "Column5", "Column6", "Column7", "Column8", "Column9", "Column10", "Column11", "Column12", "Column13", "Column14", "Column15", "Column16", "Column17", "Column18", "Column19", "Column20"}, {"all.Column2", "all.Column3", "all.Column4", "all.Column5", "all.Column6", "all.Column7", "all.Column8", "all.Column9", "all.Column10", "all.Column11", "all.Column12", "all.Column13", "all.Column14", "all.Column15", "all.Column16", "all.Column17", "all.Column18", "all.Column19", "all.Column20"})
in
    #"Expanded all"

[Anonymous]

try this

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlDSUTJUitWJBpI6SkZgFkjMGI0FkjWBi5kqxcYCAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [A = _t, B = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"A", Int64.Type}, {"B", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"A"}, {{"Count", each Table.RowCount(_), Int64.Type}},GroupKind.Local),
    #"Added Index" = Table.AddIndexColumn(#"Grouped Rows", "Index", 1, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "idx", each List.Repeat({[Index]},[Count])),
    #"Expanded idx" = Table.ExpandListColumn(#"Added Custom", "idx")
in
    #"Expanded idx"

[Anonymous]

Hello Jimmy,

Thank you very much for your kind response. Your code is successfull for a new table. But my dataset is too large. If i use it with Table.ToColumns and Table.FromColumns functions the process takes a long time. Do you have any idea about how I should use it with add.column function?

Thank you, 

[Jimmy801]

Hello @Anonymous 

is this screenshot coming from the solutions I proposed? Because the added column doesn't contain lists, but numbers. The problem with AddColumns is that you cannot refer the value of the prior row of the function. So you have to use List.Generate or List.Accumulate to produce a list, and this list you have to integrate with Table.FromColumns.

If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy

[Jimmy801 · Accepted solution]

Hello @Anonymous 

I would suggest you to do this with List.Accumulate. After you created the list that represents your index-column you have to integrate it your current table with Table.ToColumns and Table.FromColumns. Check out this example.

Give it a try and if you have performance issue we can check if we can enhance it a little bit

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlCK1YlWMgSTBkgkXCQWAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [A = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"A", Int64.Type}}),
    CreateNewIndexColumn = List.RemoveFirstN
    (
        List.Accumulate
        (
            #"Changed Type"[A],
            {1},
            (state,current)=> state & {List.Last(state) + current}
        )
    )
,

    AddIndexColumnToTable = Table.FromColumns
    (
        Table.ToColumns(#"Changed Type" ) & {CreateNewIndexColumn},
        Table.ColumnNames(#"Changed Type") & {"Index"}
    )
in
    AddIndexColumnToTable

 Copy paste this code to the advanced editor in a new blank query to see how the solution works.

If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy

[Anonymous]

Thank you @Jimmy801 it works perfect! do you have advice for how i can make it faster.

[Jimmy801]

Hello @Anonymous 

how long it runs? How big is your dataset (columns/rows?)

BR

Jimmy

[Anonymous]

@Jimmy801  Daily data contains 1.5 million rows and 20 columns. It would take about 10 minutes to get data from the server before adding this column. This time it took more than 30 minutes. When I try to get data for 2 days or more, it gives this error: Expression.Error: The evaluation resulted in a stack capacity that is exceeded and can not continue.

[Anonymous · Accepted solution]

ten millions rows worked in less than1'

let
    Source = List.Transform(List.Random(10000000), each Number.Round(_)),
    #"Converted to Table" = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Grouped Rows" = Table.Group(#"Converted to Table", {"Column1"}, {{"Count", each Table.RowCount(_), Int64.Type}},GroupKind.Local),
    #"Added Index" = Table.AddIndexColumn(#"Grouped Rows", "Index", 1, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "idx", each List.Repeat({[Index]},[Count])),
    #"Expanded idx" = Table.ExpandListColumn(#"Added Custom", "idx")
in
    #"Expanded idx"

[Anonymous]

Hello @Anonymous @

it was very useful. thank you so much.