Forum Discussion
Looping through a table in an m function
d_gosbell wrote:
It would probably have been easier to understand if you provided a few rows of example data and the output you were after.
I have now edited the original post to include a lot more detail, including this.
d_gosbell wrote:Reza has a great post on List.Accumulate here including a number of examples one of which shows using it to do a concatenate operation.
I have had a read of this page and this may work for me, I will look further into it. Thanks.
So given the edits to your question I would do this in two steps, first doing an add column to produce the row by row operation where you subtract 1000 from the year and multiply the price by 2. Then do a List.Accumulate over that column adding line breaks between each row.
eg
let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMFDSUTI1VYrVAfMMQTxzGM8IxDNQio0FAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Year = _t, Price = _t]),
#"Changed Type" = Table.TransformColumnTypes(Source,{{"Year", Int64.Type}, {"Price", Int64.Type}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each Number.ToText([Year] - 1000) & "," & Number.ToText( [Price]*2)),
Custom = #"Added Custom"[Custom],
result = List.Accumulate(Custom, "", (state, current) => state & current & "#(cr)#(lf)" )
in
resultPS. The Binary.FromText in the first line is just the pasted data from your question
Awesome! I just made Source=lineData and it all worked as expected. I will look into some of the code there and work out how it all works so I can pull it apart and use it where needed. I notice that even though we added a column here, it does not show in the table we added it to. Is this because the added column is only on the instance of the table in this function (so the variable of Source), so once the function completes it ceases to exist?
I notice that even though we added a column here, it does not show in the table we added it to. Is this because the added column is only on the instance of the table in this function (so the variable of Source), so once the function completes it ceases to exist?Yes, that's correct. The table with the added column is sort of like a tempory variable that only exists for the duration of the query. Note that it's also possible that the optimizer in PowerQuery could "fold" the logical addcolumns and accumulate steps into one physical loop over the source data (it's a pretty smart engine most of the time)
Another quick question, I send a table in as (thisTable as table)=> is it possible to send a field in that way? So in this case I have (thisTable as table, field1 as field, field2 as field)=> and would send in Year Prices as the table name, Year as field1 and Price as field2.
Or would I have to send in the field names as text and reference them that way?