Forum Discussion
Power Query List.Skip, Select
Can someone expalain why select / skip does not seem to handle errors, I have read something about
lazy evaluation whch causes the whole thing to fail; so ;
= let alist = {"a","b","c",2,2,2}
in
List.Skip( alist, (x)=>
Value.Is(x, type text) )
or
= let alist = {"a","b","c",2,2,2}
in
List.Select( alist, (x)=>
Value.Is(x, type text) )thes work as expected, but is you cause an error,
= let alist = {"a"+2,"a","c",2,2,2}
, skipper = List.Skip( alist, (x)=> not
Value.Is(x, type text) )
in skipperSo the first value = error which is not text , so why does it not skip this and then continue, and is there a way to skip or select non error values?
Richard
let alist = {"a"+2,"a","c",2,2,2}, #"Removed Errors" = Table.RemoveRowsWithErrors(Table.FromColumns({alist}))[Column1], skipper = List.Select( #"Removed Errors", each Value.Is(_, type text) ) in skipperFunction arguments are evaluated eagerily before they passed to a function body. So that your can't even use try ... otherwise from within a function to go around the error when your "x" argument in List.Skip is error itself. You need to use somthing that may contain this error - e.g. a table. This is what lbendlin did. Another example is
Table.Skip( Table.FromColumns({{"a"+2,"a","c",2,2,2}}, {"lst"}), (x) => try x[lst] is text otherwise true )[lst]Read Ben Gribaudo's Primer for more info about error handling in M.
5 Replies
let alist = {"a"+2,"a","c",2,2,2}, #"Removed Errors" = Table.RemoveRowsWithErrors(Table.FromColumns({alist}))[Column1], skipper = List.Select( #"Removed Errors", each Value.Is(_, type text) ) in skipperThanks, supprisingly tricky as it looks like quite a straighforward problem.
The basic issue is that lists don't have native error handling. If this is important to you please consider voting for an existing idea or raising a new one at https://ideas.fabric.microsoft.com
Function arguments are evaluated eagerily before they passed to a function body. So that your can't even use try ... otherwise from within a function to go around the error when your "x" argument in List.Skip is error itself. You need to use somthing that may contain this error - e.g. a table. This is what lbendlin did. Another example is
Table.Skip( Table.FromColumns({{"a"+2,"a","c",2,2,2}}, {"lst"}), (x) => try x[lst] is text otherwise true )[lst]Read Ben Gribaudo's Primer for more info about error handling in M.
Thanks, yes I had tried nesting a try / otherwise within it and as you said it don't work.
