M Code to replace underscores in column names

[teylyn]

Hi all,

my SQL Server DBA tells me that SQL doesn't like spaces in column names, and all tables and views in that project have unsightly underscores. In Power BI, I want to replace them with blanks, but changing all the column names manually is way too time consuming and doesn't scale well if more columns are added to the table or view.

Therefore, I wrote this little piece of M code that I put at the beginning of the query, just after navigating to the view or table I want. I hope that some of you find this useful.

let
  Source = Sql.Database("YourServer", "YourDatabase"),
  Navigation = Source{[Schema = "YourSchema", Item = "YourTableorView"]}[Data],
  // SQL Server doesn't like blanks in column names, so they come with underscores.
  // We replace underscores in any column name with blanks
  // list column names, turn the list into a table duplicate the name column, replace underscore with blank
  // turn the table into a list of lists
  ColumNames = Table.ColumnNames(Navigation),
  ColumnNamesTable = Table.FromList(ColumNames, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
  DuplicateColumnName = Table.DuplicateColumn(ColumnNamesTable, "Column1", "Column1 - Copy"),
  ReplaceCharacter = Table.ReplaceValue(DuplicateColumnName, "_", " ", Replacer.ReplaceText, {"Column1 - Copy"}),
  ColumnNamesList = Table.ToRows(ReplaceCharacter),
  // rename the original column names with the names from the list of lists
  RenamedColumnsFromList = Table.RenameColumns(Navigation,ColumnNamesList)
in
  RenamedColumnsFromList

Let me know how you get on with this.

cheers, teylyn

[wdx223_Daniel · Accepted solution]

Table.RenameColumns(Navigation,List.Transform(Table.ColumnNames(Navigation),each {_,Text.Replace(_,"_"," ")}))

[ImkeF]

Hi @DAXTERONPOWERBI ,
this error usually occurs when one misses a comma or didn't apply the quotes correctly. So you might want to check your M-code.

[ImkeF · Accepted solution]

Hi @teylyn  and @wdx223_Daniel ,
I've been there as well before I've discovered that the M-language has some nice functions that are not exposed through the UI. Transforming column names with a custom function is one of them: 

Table.TransformColumnNames(Source, each Text.Replace(_, "_", " ") )

[teylyn]

@wdx223_Daniel Great to see that it can be done in one step. I find the M syntax less than intuitive when it comes to writing nested formulas.

[wdx223_Daniel · Accepted solution]

Table.RenameColumns(Navigation,List.Transform(Table.ColumnNames(Navigation),each {_,Text.Replace(_,"_"," ")}))

[Rustickoff]

Works perfect! Thanks a lot!

Note: change Navigation with the name of previous step/table name and replace with Text.Replace(_," ","_") if you want to replace space with _

[DAXTERONPOWERBI]

Hi, this solution does not work instead it gives follwing error 

Expression.SyntaxError: Token Eof expected.

[Rustickoff]

I use the following to make it fit for sql:
TextLower = Table.TransformColumnNames(PreviousStepTableName, Text.Lower),

LowerDash = Table.RenameColumns( TextLower, List.Transform(Table.ColumnNames(TextLower), each {_, Text.Replace(_," ","_")}), MissingField.Ignore)

[Rustickoff]

Please kindly change Navigation with the name of previous step/table name and replace with Text.Replace(_," ","_") if you want to replace space with _