support for all basic operators, either with two columns or with one …

…column and a symbol

src/transforms.jl

@@ -200,13 +200,104 @@ function make_add_const_function(constant::Real)
 end
 
 Base.:+(s1::Symbol, s2::Symbol) = [s1, s2] => AesTransform(add_cols_fn)
-Base.:+(s1::Symbol, s2::Real) = s1 => AesTransform(make_add_const_function(s2))
-Base.:+(s2::Real, s1::Symbol) = s1 => AesTransform(make_add_const_function(s2))
-#import Base.:-
-#import Base.:/
-#import Base.:*
+Base.:+(s1::Symbol, s2::Real) = [s1] => AesTransform(make_add_const_function(s2))
+Base.:+(s2::Real, s1::Symbol) = [s1] => AesTransform(make_add_const_function(s2))
 
+import Base.:-
 
+function subtract_cols_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+    result = data[!, source[1]] .- data[!, source[2]]
+    return Dict{Symbol, PlottableData}(
+        target => PlottableData(
+            result,        
+            identity,                
+            nothing,            
+            nothing                   
+        )
+    )
+end
+
+function make_subtract_const_function(constant::Real)
+    return function add_const_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+        result = data[!, source[1]] .- constant
+        return Dict{Symbol, PlottableData}(
+            target => PlottableData(
+                result,        # get the column out of the dataframe
+                identity,      # apply generic_fn to it
+                nothing,            
+                nothing                   
+            )
+        )
+    end
+end
+
+Base.:-(s1::Symbol, s2::Symbol) = [s1, s2] => AesTransform(subtract_cols_fn)
+Base.:-(s1::Symbol, s2::Real) = [s1] => AesTransform(make_subtract_const_function(s2))
+Base.:-(s2::Real, s1::Symbol) = [s1] => AesTransform(make_subtract_const_function(s2))
+
+import Base.:/
+
+function divide_cols_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+    result = data[!, source[1]] ./ data[!, source[2]]
+    return Dict{Symbol, PlottableData}(
+        target => PlottableData(
+            result,        
+            identity,                
+            nothing,            
+            nothing                   
+        )
+    )
+end
+
+function make_divide_const_function(constant::Real)
+    return function add_const_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+        result = data[!, source[1]] ./ constant
+        return Dict{Symbol, PlottableData}(
+            target => PlottableData(
+                result,        # get the column out of the dataframe
+                identity,      # apply generic_fn to it
+                nothing,            
+                nothing                   
+            )
+        )
+    end
+end
+
+Base.:/(s1::Symbol, s2::Symbol) = [s1, s2] => AesTransform(divide_cols_fn)
+Base.:/(s1::Symbol, s2::Real) = [s1] => AesTransform(make_divide_const_function(s2))
+Base.:/(s2::Real, s1::Symbol) = [s1] => AesTransform(make_divide_const_function(s2))
+
+import Base.:*
+
+function multiply_cols_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+    result = data[!, source[1]] .* data[!, source[2]]
+    return Dict{Symbol, PlottableData}(
+        target => PlottableData(
+            result,        
+            identity,                
+            nothing,            
+            nothing                   
+        )
+    )
+end
+
+function make_multiply_const_function(constant::Real)
+    return function add_const_fn(target::Symbol, source::Vector{Symbol}, data::DataFrame)
+        result = data[!, source[1]] .* constant
+        return Dict{Symbol, PlottableData}(
+            target => PlottableData(
+                result,        # get the column out of the dataframe
+                identity,      # apply generic_fn to it
+                nothing,            
+                nothing                   
+            )
+        )
+    end
+end
+
+Base.:*(s1::Symbol, s2::Symbol) = [s1, s2] => AesTransform(multiply_cols_fn)
+Base.:*(s1::Symbol, s2::Real) = [s1] => AesTransform(make_multiply_const_function(s2))
+Base.:*(s2::Real, s1::Symbol) = [s1] => AesTransform(make_multiply_const_function(s2))
 
 
 # tweaks