Table Transformations for Dynamic Columns

[Anonymous]

Hi,

Input:

I have a table with changing #'s of columns.

Process:

I need to take the first two characters of these columns. So I need PQ to dynamically identify which columns to take the first two characters from depending on their header name. For instance, something like for all columns that start with ABCD, take the first two characters of every row.

Problem:

I know how to make a list of the headers that start with ABCD. But I don't know how to pass that list to a TableTransformColumns_Text.Start(ColumnList, 2). Where columnlist is Power BI only seems to accept 1 column value at a time, and if more are desired the code needs to be repeated with the new column name which of course won't work dynamically.

Any ideas on how to pass dynamic column amounts through a table transformation text.start? Thanks!

For ex: The below code works with removing columns dynamically. Something like this but with Text.Start

    Source = Table.FromRows({{"New York", 23, 51, 732}, {"Chicago", 25, 421, 23}, {"Los Angeles", 632, 22, 423}}, {"City", "Value 1", "Value 2", "Column 3"}),
    ColumnsToRemove = List.Select(Table.ColumnNames(Source), each Text.StartsWith(_, "V")),
    RemovedColumns = Table.RemoveColumns(Source, ColumnsToRemove)

Thanks,

Buri 

[Zubair_Muhammad · Accepted solution]

HI @Anonymous

If I understand the problem correctly

Suppose in your above sample, you want to transform the Columns starting with V

for example multiply all values by 10 or divide them by 10 you can use something like this

let
Source = Table.FromRows({{"New York", 23, 51, 732}, {"Chicago", 25, 421, 23}, {"Los Angeles", 632, 22, 423}}, {"City", "Value 1", "Value 2", "Column 3"}),
ColumnsToTransform= List.Select(Table.ColumnNames(Source), each Text.StartsWith(_, "V")),
ActionToPerform=List.Repeat({each _ *10},List.Count(ColumnsToTransform)),
Transformed=Table.TransformColumns(Source,List.Zip({ColumnsToTransform,ActionToPerform}))
in
 Transformed

[Greg_Deckler]

I do not but @ImkeF might.

[ImkeF · Accepted solution]

Please try this function:

(InputTable as table, ListOfColNames, TransformFunction as function) =>
let
    TransformFunctionList = List.Transform(ListOfColNames, (x) => {x, TransformFunction}),
    Transform = Table.TransformColumns(InputTable, TransformFunctionList)
in
    Transform

Name it "fnTransformMany" and call it like so:

let
    Source = Table.FromRows({{"New York", "23", "51", "732"}, {"Chicago", "25", "421", "23"}, {"Los Angeles", "632", "22", "423"}}, {"City", "Value 1", "Value 2", "Column 3"}),
    ColumnsToRemove = List.Select(Table.ColumnNames(Source), each Text.StartsWith(_, "V")),
    Result = fnTransformMany(Source, ColumnsToRemove, each Text.Start(_, 2))
in
    Result

[Anonymous]

@ImkeF, @Zubair_Muhammad, @Greg_Deckler - Thank you so much. You all are awesome and I really appreciate the help. Brilliant solutions!

[Zubair_Muhammad · Accepted solution]

HI @Anonymous

If I understand the problem correctly

Suppose in your above sample, you want to transform the Columns starting with V

for example multiply all values by 10 or divide them by 10 you can use something like this

let
Source = Table.FromRows({{"New York", 23, 51, 732}, {"Chicago", 25, 421, 23}, {"Los Angeles", 632, 22, 423}}, {"City", "Value 1", "Value 2", "Column 3"}),
ColumnsToTransform= List.Select(Table.ColumnNames(Source), each Text.StartsWith(_, "V")),
ActionToPerform=List.Repeat({each _ *10},List.Count(ColumnsToTransform)),
Transformed=Table.TransformColumns(Source,List.Zip({ColumnsToTransform,ActionToPerform}))
in
 Transformed