at
The keyword at is a process option in Envision.
‘proc(..) by (expr) at (expr)’
The by .. at syntax is a call option is used to control the output table of a process.
table Origins = with
[| as Origin |]
[| "France" |]
[| "Italy" |]
[| "Spain" |]
table Routes = with
[| as Destination, as Origin |]
[| "USA", "France" |]
[| "Germany", "Spain" |]
[| "Germany", "Italy" |]
table Shipments = with
[| as Destination, as Origin, as OrderDate, as Quantity |]
[| "USA", "France", date(2020, 4, 15), 3 |]
[| "Germany", "Spain", date(2020, 4, 16), 6 |]
[| "Germany", "Italy", date(2020, 4, 16), 2 |]
[| "USA", "France", date(2020, 4, 17), 5 |]
[| "Germany", "Spain", date(2020, 4, 18), 1 |]
Origins.Incoming = sum(Shipments.Quantity) by Shipments.Origin at Origins.Origin
Routes.Incoming = sum(Shipments.Quantity) // implicit line continuation
by [Shipments.Destination, Shipments.Origin] // tuple with `[.. , ..]`
at [Routes.Destination, Routes.Origin]
show table "Incoming by Origin" with Origins.Origin, Origins.Incoming
// Origin, Incoming
// France, 8
// Italy, 2
// Spain, 7
show table "Incoming by Route" with Routes.Destination, Routes.Origin, Routes.Incoming
// Destination, Origin, Incoming
// USA, France, 8
// Germany, Spain, 7
// Germany, Italy, 2
The by-at allows to process the data from a table T1 to a table T2 even if the two tables are otherwise unrelated.
The usual intent with Envision is to avoid by-at by leveraging the relationships between the tables.
table Origins[orig] = with
[| as orig |]
[| "France" |]
[| "Italy" |]
[| "Spain" |]
table Shipments = with
[| as Destination, as Origin, as OrderDate, as Quantity |]
[| "USA", "France", date(2020, 4, 15), 3 |]
[| "Germany", "Spain", date(2020, 4, 16), 6 |]
[| "Germany", "Italy", date(2020, 4, 16), 2 |]
[| "USA", "France", date(2020, 4, 17), 5 |]
[| "Germany", "Spain", date(2020, 4, 18), 1 |]
expect Shipments.orig = Shipments.Origin // add 'orig' as a secondary dimension to 'Shipments'
Origins.Incoming = sum(Shipments.Quantity) // implicit 'by-at' using the secondary dimension
show table "Incoming by Origin" with orig as "Origin", Origins.Incoming
// Origin, Incoming
// France, 8
// Italy, 2
// Spain, 7
Indeed, a script that aggregates data from table T1 to table T2 is likely to do so many times. Defining a relationship removes the need to specify the by-at every single time.