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Diffstat (limited to 'src/operations.erl')
| -rw-r--r-- | src/operations.erl | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/src/operations.erl b/src/operations.erl new file mode 100644 index 0000000..7846caf --- /dev/null +++ b/src/operations.erl @@ -0,0 +1,15 @@ +-module(operations). +-export([select/2, project/2, cartesian_product/2]). + +%% @doc Selection - filter tuples based on a predicate +%% `Predicate` is a function that takes a tuple and returns true/false +select(Relation, Predicate) -> + sets:filter(Predicate, Relation). + +%% @doc Projection - select specific attributes from a relation +%% Note that `AttributeNames` can have duplicate keys, which are ignored +project(Relation, AttributeNames) when is_list(AttributeNames) -> + sets:map(fun (Tuple) -> maps:with(AttributeNames, Tuple) end, Relation). + +cartesian_product(Relation1, Relation2) -> + sets:from_list([maps:merge(Tuple1, Tuple2) || Tuple1 <- sets:to_list(Relation1), Tuple2 <- sets:to_list(Relation2)], [{version, 2}]). |