[Rd] as.integer(x) versus as.integer(trunc(x))

[Petr Savicky]

as.integer(x) rounds floating point numbers towards zero,
so it behaves approximately as as.integer(trunc(x)).

If x > INT_MAX, then as.integer(x) is NA. This is nothing
bad, but it is slightly more restrictive than necessary. An
alternative approach could be that
  as.integer(x) is NA, if trunc(x) > INT_MAX and
  as.integer(x) == INT_MAX for all x in [INT_MAX,INT_MAX+1).

Let me suggest the following patch to IntegerFromReal for consideration:

--- R-devel_2007-10-11-orig/src/main/coerce.c	2007-07-25 17:54:17.000000000 +0200
+++ R-devel_2007-10-11-asinteger/src/main/coerce.c	2007-10-12 07:10:06.000000000 +0200
@@ -173,7 +173,8 @@
 {
     if (ISNAN(x))
 	return NA_INTEGER;
-    else if (x > INT_MAX || x <= INT_MIN ) {
+    x = trunc(x);
+    if (x > INT_MAX || x <= INT_MIN ) {
 	*warn |= WARN_NA;
 	return NA_INTEGER;
     }

This patch changes the behavior as suggested above. Its effect may be seen
using the script
  options(digits=12)
  x <- seq(2^31 - 3, 2^31, length=7)
  cbind(x,as.integer(trunc(x)),as.integer(x))

Original behavior:
  [1,] 2147483645.0 2147483645 2147483645
  [2,] 2147483645.5 2147483645 2147483645
  [3,] 2147483646.0 2147483646 2147483646
  [4,] 2147483646.5 2147483646 2147483646
  [5,] 2147483647.0 2147483647 2147483647
  [6,] 2147483647.5 2147483647         NA
  [7,] 2147483648.0         NA         NA

Using the patch:
  [1,] 2147483645.0 2147483645 2147483645
  [2,] 2147483645.5 2147483645 2147483645
  [3,] 2147483646.0 2147483646 2147483646
  [4,] 2147483646.5 2147483646 2147483646
  [5,] 2147483647.0 2147483647 2147483647
  [6,] 2147483647.5 2147483647 2147483647
  [7,] 2147483648.0         NA         NA

Petr Savicky.