incorporate @thirdwing's suggestion for sugar ops (closes #392)

Author: kevinushey

.gitignore

@@ -4,6 +4,7 @@ src/*.o
 src/*.so
 src/*.dll
 .Rhistory
+.RData
 
 ## QtCreator
 Rcpp.pro

ChangeLog

@@ -1,3 +1,10 @@
+2015-11-06  Kevin Ushey <kevinushey@gmailcom>
+
+        * inst/include/Rcpp/vector/Subsetter.h: Add sugar math operators
+        * inst/unitTests/runit.subset.R: Unit tests
+        * inst/unitTests/cpp/Subset.cpp: Unit tests
+        * inst/NEWS.Rd: NEWS entry
+
 2015-11-01  Qiang Kou <[email protected]>
 
         * inst/include/Rcpp/vector/MatrixColumn.h: Fix overflow

inst/NEWS.Rd

@@ -24,6 +24,8 @@
     \itemize{
       \item Added new Sugar function \code{cummin()}, \code{cummax()},
       \code{cumprod()} (PR \ghpr{389} by Nathan Russell fixing \ghit{388})
+      \item Enabled sugar math operations for subsets; e.g. x[y] + x[z].
+      (PR \ghpr{393}, implementing \ghit{392})
     }
     \item Changes in Rcpp Documentation:
     \itemize{

inst/include/Rcpp/vector/Subsetter.h

@@ -226,6 +226,33 @@ class SubsetProxy {
     // because of the above, we keep track of the size
     int indices_n;
 
+public:
+
+#define RCPP_GENERATE_SUBSET_PROXY_OPERATOR(__OPERATOR__)                      \
+    template <int RTYPE_OTHER, template <class> class StoragePolicyOther,      \
+              int RHS_RTYPE_OTHER, bool RHS_NA_OTHER, typename RHS_T_OTHER>    \
+    SubsetProxy& operator __OPERATOR__ (                                       \
+        const SubsetProxy<RTYPE_OTHER, StoragePolicyOther, RHS_RTYPE_OTHER,    \
+                          RHS_NA_OTHER, RHS_T_OTHER>& other) {                 \
+        if (other.indices_n == 1) {                                            \
+            for (int i = 0; i < indices_n; ++i)                                \
+                lhs[indices[i]] __OPERATOR__ ## = other.lhs[other.indices[0]]; \
+        } else if (indices_n == other.indices_n) {                             \
+            for (int i = 0; i < indices_n; ++i)                                \
+                lhs[indices[i]] __OPERATOR__ ## = other.lhs[other.indices[i]]; \
+        } else {                                                               \
+            stop("index error");                                               \
+        }                                                                      \
+        return *this;                                                          \
+    }
+
+RCPP_GENERATE_SUBSET_PROXY_OPERATOR(+)
+RCPP_GENERATE_SUBSET_PROXY_OPERATOR(-)
+RCPP_GENERATE_SUBSET_PROXY_OPERATOR(*)
+RCPP_GENERATE_SUBSET_PROXY_OPERATOR(/)
+
+#undef RCPP_GENERATE_SUBSET_PROXY_OPERATOR
+
 };
 
 }

inst/unitTests/cpp/Subset.cpp

@@ -102,3 +102,10 @@ NumericVector subset_assign_vector_size_1(NumericVector x, int i) {
     return x;
 }
 
+// [[Rcpp::export]]
+NumericVector subset_sugar_add(NumericVector x, IntegerVector y)
+{
+    NumericVector result = x[y] + x[y];
+    return result;
+}
+

inst/unitTests/runit.subset.R

@@ -86,6 +86,10 @@ if (.runThisTest) {
         checkException(subset_assign_subset5(1:6), msg = "index error")
 
         checkIdentical(subset_assign_vector_size_1(1:6,7), c(7,7,7,4,5,6))
+
+        x <- rnorm(10)
+        y <- sample(10, 5)
+        checkIdentical(subset_sugar_add(x, y - 1L), x[y] + x[y])
     }
 
 }