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ListRelation Subscription

rascal-0.40.17

Synopsis​

Indexing of a list relation via tuple values.

Syntax​

  • Exp₀ [ Exp₁, Exp₂, ... Expₙ]

  • Exp₀ [ Exp₁]

Variant 1​

Exp₀Exp₁Exp₂...Exp₀ [ Exp₁, Exp₂, ... ]
lrel[T₁, T₂, ... Tₘ]intint...lrel[Tₙ, _Tₙ₊₁_, ... Tₘ]

Variant 2​

Exp₀Exp₁Exp₀ [ Exp₁ ]

| | lrel[T₁, T₂, ... Tₘ] | list[T₁] | lrel[T₂, T₃, ... Tₘ] |

Description​

ListRelation resulting from subscription of a ListRelation Exp₀.

Variant 1​

Subscription with the index values of Exp₁, Exp₂, .... The result is a ListRelation 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 list is returned instead of a relation. A wildcard _ as index value matches all possible values at that index position.

Variant 2​

Subscription with a set of the index values of Exp₁. The result is a ListRelation 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>];
lrel[int,int]: [
  <1,10>,
  <2,20>,
  <1,11>,
  <3,30>,
  <2,21>
]
rascal>R[1];
tuple[int,int]: <2,20>
rascal>R[{1}];
list[int]: [10,11]
rascal>R[{1, 2}];
list[int]: [10,20,11,21]
rascal>RR = [<1,10,100>,<1,11,101>,<2,20,200>,<2,22,202>,
>>>>>>>              <3,30,300>];
lrel[int,int,int]: [
  <1,10,100>,
  <1,11,101>,
  <2,20,200>,
  <2,22,202>,
  <3,30,300>
]
rascal>RR[1];
tuple[int,int,int]: <1,11,101>
rascal>RR[1,_];
list[int]: [100,101]

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

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

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

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

or rather for the indices "Japan" and 2008:

rascal>GDP["Japan", 2008];
list[int]: [4923761]