Add RDF.Description.take/2

CHANGELOG.md

@@ -5,6 +5,19 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 [Keep a CHANGELOG](http://keepachangelog.com).
 
 
+## Unreleased
+
+### Added
+
+- `RDF.Description.take/2` creates a description from another one by limiting 
+  its statements to a set of predicates
+- Mix formatter configuration for using `defvocab` without parens 
+
+
+[Compare v0.6.2...HEAD](https://github.com/marcelotto/rdf-ex/compare/v0.6.2...HEAD)
+
+
+
 ## 0.6.2 - 2019-09-08
 
 ### Added

lib/rdf/description.ex

@@ -616,6 +616,15 @@ defmodule RDF.Description do
     end
   end
 
+  @doc """
+  Creates a description from another one by limiting its statements to those using one of the given `predicates`.
+
+  If `predicates` contains properties that are not used in the `description`, they're simply ignored.
+  """
+  def take(%RDF.Description{predications: predications} = description, predicates) do
+    predicates = Enum.map(predicates, &(coerce_predicate/1))
+    %RDF.Description{description | predications: Map.take(predications, predicates)}
+  end
 
   @doc """
   Checks if two `RDF.Description`s are equal.

test/unit/description_test.exs

@@ -144,7 +144,6 @@ defmodule RDF.DescriptionTest do
       refute description_includes_predication(desc, {EX.predicate, iri(EX.Object3)})
     end
 
-
     test "another description" do
       desc = description([{EX.predicate1, EX.Object1}, {EX.predicate2, EX.Object2}])
         |> Description.add(Description.new({EX.Other, EX.predicate3, EX.Object3}))
@@ -358,6 +357,12 @@ defmodule RDF.DescriptionTest do
              %{p: ["Foo"]}
   end
 
+  test "take/2" do
+    assert Description.new([{EX.S, EX.p1, EX.O1}, {EX.S, EX.p2, EX.O2}])
+           |> Description.take([EX.p2, EX.p3]) ==
+             Description.new({EX.S, EX.p2, EX.O2})
+  end
+
   test "equal/2" do
     assert Description.new({EX.S, EX.p, EX.O}) |> Description.equal?(Description.new({EX.S, EX.p, EX.O}))
     refute Description.new({EX.S, EX.p, EX.O}) |> Description.equal?(Description.new({EX.S, EX.p, EX.O2}))