Add gather macro

src/Query.jl

@@ -9,7 +9,7 @@ using QueryOperators
 export @from, @query, @count, Grouping, key
 
 export @map, @filter, @groupby, @orderby, @orderby_descending, @unique,
-	@thenby, @thenby_descending, @groupjoin, @join, @mapmany, @take, @drop
+	@thenby, @thenby_descending, @groupjoin, @join, @mapmany, @take, @drop, @gather
 
 export @select, @rename, @mutate
 

src/standalone_query_macros.jl

@@ -182,6 +182,19 @@ macro map(f)
         helper_namedtuples_replacement
 end
 
+macro gather(args...)
+    parsedArgs = ()
+    for arg in args
+        if typeof(arg) == Expr
+            m1 = match(r"^-:(.+)", string(arg))
+            parsedArgs = (parsedArgs..., :(QueryOperators.Not($(QuoteNode(Symbol(m1[1]))))))
+        else
+            parsedArgs = (parsedArgs..., arg)
+        end
+    end
+    :( i -> QueryOperators.gather(QueryOperators.query(i), $(parsedArgs...)))
+end
+
 macro mapmany(source, collectionSelector,resultSelector)
     collectionSelector_as_anonym_func = helper_replace_anon_func_syntax(collectionSelector)
     resultSelector_as_anonym_func = helper_replace_anon_func_syntax(resultSelector)

test/runtests.jl

@@ -493,6 +493,7 @@ q = collect(@map(source_df, i->i.children))
 
 include("test_dplyr-syntax.jl")
 include("test_pipesyntax.jl")
+include("test_standalone.jl")
 include("test_macros.jl")
 
 end

test/test_standalone.jl

@@ -1,4 +1,5 @@
 using Query
+using QueryOperators
 using DataFrames
 using Test
 
@@ -44,6 +45,23 @@ end
     @test df2[:c] == ["b","c"]
 end
 
+@testset "@gather operator" begin
+    source_gather = DataFrame(Year=[2017,2018,2019], US=[1,2,3], EU=[4,5,6], CN=[7,8,9])
+    @test source_gather |> @gather(:US, :EU, :CN) |> collect ==
+        [
+            (Year = 2017, key = :US, value = 1), 
+            (Year = 2017, key = :EU, value = 4),
+            (Year = 2017, key = :CN, value = 7),
+            (Year = 2018, key = :US, value = 2),
+            (Year = 2018, key = :EU, value = 5),
+            (Year = 2018, key = :CN, value = 8),
+            (Year = 2019, key = :US, value = 3),
+            (Year = 2019, key = :EU, value = 6),
+            (Year = 2019, key = :CN, value = 9)
+        ]
+    @test eltype(source_gather |> @gather(:US, :EU, :CN)) == NamedTuple{(:Year, :key, :value),Tuple{Int, Symbol, Int}}
+end
+
 @testset "@unique operator" begin
     df = DataFrame(a=[1,2,1], b=[3.,3.,3.])