Merge pull request #3 from davidagold/select

Solution to issue #2

src/groupby.jl

@@ -1,7 +1,27 @@
-macro groupby(fields...)
-    g = _groupby(gensym(), collect(fields))
+#=
+@groupby experiences same issue concerning piped and non-piped data inputs as
+does @select. See top of `src/select.jl` for details and current solution
+=#
+macro groupby(args...)
+    # for case where first arg is data input
+    input, cols = args[1], args[2:end]
+    _input = QuoteNode(input)
+    g1 = _groupby(input, collect(cols))
+    # for case where all args are column specifications
+    g2 = _groupby(gensym(), collect(args))
     return quote
-        run($g)
+        try # assume first that first arg is data input
+            run($(esc(input)), $g1)
+        catch err
+            #= if error because first arg isn't valid name, assume it is a
+            column specification and return curried run. Otherwise, throw
+            the error =#
+            if err == UndefVarError($_input)
+                run($g2)
+            else
+                throw(err)
+            end
+        end
     end
 end
 

src/select.jl

@@ -1,13 +1,34 @@
 #=
-TO DO: figure out how to differentiate b/w piped to and non-piped to
-@select calls. Currently, only the former are handled. The issue is how to
-distinguish a symbol that represents a data source argument from a symbol
-that represents a field name argument
+OPEN QUESTION: How to differentiate b/w piped to and non-piped to
+@select calls. The issue is how to distinguish a symbol that represents a
+data source argument from a symbol that represents a column specification.
+The following is one way to do so. However, this strategy will fail/give
+incorrect results in cases such as the following:
+
+df |> @select(fieldname)
+
+where `df` and `fieldname` are both valid names bound to DataFrame objects.
 =#
-macro select(syms...)
-    g = _select(gensym(), collect(syms))
+macro select(args...)
+    # for case where first arg is data input
+    input, cols = args[1], args[2:end]
+    _input = QuoteNode(input)
+    g1 = _select(input, collect(cols))
+    # for case where all args are column specifications
+    g2 = _select(gensym(), collect(args))
     return quote
-        run($g)
+        try # assume first that first arg is data input
+            run($(esc(input)), $g1)
+        catch err
+            #= if error because first arg isn't valid name, assume it is a
+            column specification and return curried run. Otherwise, throw
+            the error =#
+            if err == UndefVarError($_input)
+                run($g2)
+            else
+                throw(err)
+            end
+        end
     end
 end