Forum Discussion
Dynamically Merge Multiple Columns
Hi all, I want to dynamically merge columns in a function.
Let's say I have this fairly 'standard' PQ expression:
#"Inserted Merged Column" = Table.AddColumn(#"PreviousStepp", "NewColumnName", each Text.Combine({[Column1], [Column2]}, "."), type text)
The result would be:
| Column1 | Column2 | NewColumnName |
| A | B | A.B |
| C | D | C.D |
Now, I'd like to make this expression dynamic in a function where I pass the columns to be merged. So the code might look like this:
(ColumnNamesList as list) =>
#"Inserted Merged Column" = Table.AddColumn(#"PreviousStepp", "NewColumnName", each Text.Combine(ColumnNamesList, "."), type text)
The problem is that Text.Combin expects an explict column name reference bracketed i.e. '[Column1]'.
Whereas the list will pass a list of Text values that are not converted to expclit column references (even if brackets are included)
i.e. this list will not work
| List |
| [Column1] |
| [Column2] |
It will be passed as {"[Column1]", "[Column2]"} and Text.Combine will fail.
How do I dymically pass a list of column name references that will function with the Text.Combine and respect the 'each' iterator for the rows? Normally I would use:
Record.Field(_, varColumnName)
But I don't know how to dynamically expand that expression to iterate Record.Field over each Column in the list?
Here is one way to do it. You can provide the colnames as a concatenated text string and parse it in the function.
//fnAddMergeColumn let Source = (inputtable as table, newcolumn as text, colnames as text) => let result = Table.AddColumn(inputtable, "Concatenated", each Text.Combine(Record.ToList(Record.SelectFields(_, Text.Split(colnames, "-")) ), ".")) in result in Source
5 Replies
Here is one way to do it. You can provide the colnames as a concatenated text string and parse it in the function.
//fnAddMergeColumn let Source = (inputtable as table, newcolumn as text, colnames as text) => let result = Table.AddColumn(inputtable, "Concatenated", each Text.Combine(Record.ToList(Record.SelectFields(_, Text.Split(colnames, "-")) ), ".")) in result in Sourceok, this has me thinking... and I think this is kinda of what your code is doing.
I could use my Text list of of column names to isolate the columns I'm interested in merging into a seperate table, as a Table I should be able to just merge all the associate columns, then pass the merged values as a column back into my original table through a merge. Will tackle this further in the morning.
Hi rpiboy_1
I don't see the advantage of creating another function to do this. At some point you have to declare what ColumnNamesList is so not sure how 'dynamic' your desired solution is.
Why not just concatenate the columns ?
= [Column1] & "." & [Column2]Regards
Phil
FYI, to close the loop on this. I did not end up writing this as a seperate function, but it was helpful to see the solution written as a stand-alone function from the perspective of parsing the code to understand how to adopt it to my own needs.
I was actually able to drop the 'Text.Split' as in my real function I already have the columns names as list, so conviently I'm able to just pass that list directly and it all works!
Thanks again!
