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Relation Subscription

rascal-0.40.17

Syntax​

  • Exp₀ [Exp₁, Exp₂, ..., Expₙ]
  • Exp₀ [Exp₁]

Synopsis​

Indexing of a relation via tuple values.

Single Value Variant 1​
_Exp₀Exp₁Exp₂...Exp0_ [ Exp₁, Exp₂, ... ]
rel[T₁, T₂, ... Tₘ]intint...rel[Tₙ, _Tₙ₊₁_, ... Tₘ]
Set of Values Variant​
Exp₀Exp₁Exp₀ [ Exp₁ ]
rel[T₁, T₂, ... Tₘ]set[T₁]rel[T₂, T₂, ... Tₘ]

Description​

Relation resulting from subscription of a relation Exp₀.

Single Value Variant​

Subscription with the index values of Exp₁, Exp₂, .... The result is a relation with all tuples that have these index values as first elements with the index values removed from the tuple. If the resulting tuple has only a single element, a set is returned instead of a relation. A wildcard _ as index value matches all possible values at that index position.

Set of Values Variant​

Subscription with a set of the index values of Exp₁. The result is a relation with all tuples that have these index values as first element with the index values removed from the tuple.

Examples​

rascal>R = {<1,10>, <2,20>, <1,11>, <3,30>, <2,21>};
rel[int,int]: {
  <3,30>,
  <1,10>,
  <1,11>,
  <2,20>,
  <2,21>
}
rascal>R[1];
set[int]: {10,11}
rascal>R[{1}];
set[int]: {10,11}
rascal>R[{1, 2}];
set[int]: {10,20,11,21}
rascal>RR = {<1,10,100>,<1,11,101>,<2,20,200>,<2,22,202>,
>>>>>>>              <3,30,300>};
rel[int,int,int]: {
  <1,10,100>,
  <3,30,300>,
  <1,11,101>,
  <2,20,200>,
  <2,22,202>
}
rascal>RR[1];
rel[int,int]: {
  <10,100>,
  <11,101>
}
rascal>RR[1,_];
set[int]: {100,101}

Introduce a relation with economic data and assign it to GDP:

rascal>rel[str country, int year, int amount] GDP =
>>>>>>>{<"US", 2008, 14264600>, <"EU", 2008, 18394115>,
>>>>>>> <"Japan", 2008, 4923761>, <"US", 2007, 13811200>, 
>>>>>>> <"EU", 2007, 13811200>, <"Japan", 2007, 4376705>};
rel[str country,int year,int amount]: {
  <"EU",2007,13811200>,
  <"US",2007,13811200>,
  <"Japan",2007,4376705>,
  <"US",2008,14264600>,
  <"Japan",2008,4923761>,
  <"EU",2008,18394115>
}

and then retrieve the information for the index "Japan":

rascal>GDP["Japan"];
rel[int,int]: {
  <2007,4376705>,
  <2008,4923761>
}

or rather for the indices "Japan" and 2008:

rascal>GDP["Japan", 2008];
set[int]: {4923761}