add resizeVector and export at C level

inst/tests/tests.Rraw

@@ -85,6 +85,8 @@ if (exists("test.data.table", .GlobalEnv, inherits=FALSE)) {
   which.last = data.table:::which.last
   `-.IDate` = data.table:::`-.IDate`
   haszlib = data.table:::haszlib
+  CcopyAsGrowable = data.table:::CcopyAsGrowable
+  CresizeVector = data.table:::CresizeVector
 
   # Also, for functions that are masked by other packages, we need to map the data.table one. Or else,
   # the other package's function would be picked up. As above, we only need to do this because we desire
@@ -21775,3 +21777,23 @@ test(2377.44, copy(dt)[!(a < 5 & b != "d"), .ROW := NULL], dt[1:3])
 dt = data.table(a=1:3)
 test(2377.91, truelength(dt$a), 0L)
 test(2377.92, {setallocrow(dt); truelength(dt$a)}, 3L)
+
+# test R C API via data.table #7810
+set.seed(108)
+x = rnorm(100L)
+test(2378.01, length(x) == 100L && truelength(x) == 0L)
+x = .Call(CcopyAsGrowable, x)
+test(2378.02, length(x) == 100L && truelength(x) == 100L)
+invisible(.Call(CresizeVector, x, 50L))
+test(2378.03, length(x) == 50L && truelength(x) == 100L)
+invisible(.Call(CresizeVector, x, 0L))
+test(2378.04, length(x) == 0L && truelength(x) == 100L)
+invisible(.Call(CresizeVector, x, 49L))
+test(2378.05, length(x) == 49L && truelength(x) == 100L)
+invisible(.Call(CresizeVector, x, 51L))
+test(2378.06, length(x) == 51L && truelength(x) == 100L)
+test(2378.91, .Call(CresizeVector, x, 2), error = "must be length 1 non-NA non-negative integer value")
+test(2378.92, .Call(CresizeVector, x, 2:3), error = "must be length 1 non-NA non-negative integer value")
+test(2378.93, .Call(CresizeVector, x, -2L), error = "must be length 1 non-NA non-negative integer value")
+test(2378.94, .Call(CresizeVector, x, NA_integer_), error = "must be length 1 non-NA non-negative integer value")
+test(2378.95, .Call(CresizeVector, NULL, 2L), error = "must be a vector")

src/data.table.h

@@ -308,6 +308,7 @@ SEXP memcpyDT(SEXP dest, SEXP src, SEXP offset, SEXP size);
 SEXP memcpyVectoradaptive(SEXP dest, SEXP src, SEXP offset, SEXP size);
 SEXP memcpyDTadaptive(SEXP dest, SEXP src, SEXP offset, SEXP size);
 SEXP copyAsGrowable(SEXP x);
+SEXP resizeVector(SEXP x, SEXP size);
 
 // nafill.c
 void nafillDouble(double *x, uint_fast64_t nx, unsigned int type, double fill, bool nan_is_na, ans_t *ans, bool verbose);

src/frollapply.c

@@ -87,3 +87,14 @@ SEXP copyAsGrowable(SEXP x) {
   UNPROTECT(1);
   return ret;
 }
+
+SEXP resizeVector(SEXP x, SEXP size) {
+  if (!(
+    isInteger(size) && LENGTH(size) == 1 && INTEGER_RO(size)[0] >= 0
+  )) error(_("'size' must be length 1 non-NA non-negative integer value."));
+  if (!isVector(x))
+    error(_("'x' must be a vector."));
+  R_xlen_t newlen = INTEGER_RO(size)[0];
+  R_resizeVector(x, newlen);
+  return x;
+}

src/init.c

@@ -161,6 +161,7 @@ static const R_CallMethodDef callMethods[] = {
     {"CmemcpyVectoradaptive", (DL_FUNC)&memcpyVectoradaptive, -1},
     {"CmemcpyDTadaptive", (DL_FUNC)&memcpyDTadaptive, -1},
     {"CcopyAsGrowable", (DL_FUNC)&copyAsGrowable, -1},
+    {"CresizeVector", (DL_FUNC)&resizeVector, -1},
     {"Cfrolladapt", (DL_FUNC)&frolladapt, -1},
     {"Cis_direct_child", (DL_FUNC)&is_direct_child, -1},
     {NULL, NULL, 0}};