How can I concatenate grouped values in PowerQuery

Question

If I have this table, how can I write a grouped query that would concatenate the grouped results?

For instance, I'd want to group by the LetterColumn and concatenate the NumberColumn

So, the desired output is:

Answer 1

If your table is Source, and if NumberColumn has the number type, then this will work:

= Table.Group(Source, {"LetterColumn"}, {{"Column", each Text.Combine(List.Transform(_[NumberColumn], (x) => Number.ToText(x)), ","), type text}})

Table.Group does a group by operation, which creates a table made up of all of the rows with the same value in LetterColumn. _[NumberColumn] gives a list of the values in the NumberColumn column in this new table. The List.Transform part turns the numbers into text values, and Text.Combine joins those numbers together, with a comma separating each value.

If you need the surrounding quotes as well, you can do this:

= Table.Group(Source, {"LetterColumn"}, {{"Column", each """" & Text.Combine(List.Transform(_[NumberColumn], (x) => Number.ToText(x)), ",") & """", type text}})

"""" represents the " character, and & combines two text values.