Forum Discussion
Post ProdigyTransform columns / type
Hi Dicken,
When you write:
Table.TransformColumns(Source, {"anumber", Number.From})you are passing Power Query the built-in Number.From function directly. Because that function has a known return type of number, Power Query can often detect that and update the column’s type automatically.
When you write:
Table.TransformColumns(Source, {"anumber", each Number.From(_)})you are creating a new inline anonymous function. Even though it calls Number.From, that function itself is untyped. As a result, only the values are converted.
To ascribe type explicitly when using each, pass the new column type as third argument:
Table.TransformColumns(Source, {"anumber", each Number.From(_), type number})When you write:
ascribeNum = (x) as number => Number.From(x),
transform = Table.TransformColumns(Source, {"anumber", ascribeNum})you are creating a new function with a return type of number. Like when passing the built-in Number.From function directly, Power Query can often detect that and update the column’s type.I hope this is helpful.
In the third parameter you can specify the column type
Why does Power Query behave this way? Is it because of "lazy evaluation"
Post Prodigyregarding adding a column type ; you can pre build that as ;
{ "atext", each Text.From(_), Text.Type }
then if you have multiple use zip; so ;
= let f = { each Text.From(_), each Number.From(_), each Int64.From(_), each Logical.From(_)},
tipe = { Text.Type, Number.Type, Int64.Type, Logical.Type }
in
List.Zip( { Table.ColumnNames( Source) , f, tipe } )
then
= Table.TransformColumns( Source, ziplist )
Super UserIf you are studying column typing, here are the options
let
lst = List.LastN(Table.ColumnNames(Source), 2),
Source = #table(
type table [sometext = Any.Type, anumber = Any.Type, aint = Any.Type],
{{"cat", 10.5, 12}}
),
Custom1 = Table.TransformColumns(
Source,
List.Transform(lst, (x) => {x, Number.From, type number})
)
in
Custom1
----------------
let
lst = List.LastN(Table.ColumnNames(Source), 2),
Source = #table(
type table [sometext = Any.Type, anumber = Any.Type, aint = Any.Type],
{{"cat", 10.5, 12}}
),
Custom1 = Table.TransformColumns(
Source,
List.Transform(lst, (x) => {x, (x) as nullable number => Number.From(x)})
)
in
Custom1