reinstate np loop but use truncation

Author: hturner

src/library/base/R/datetime.R

@@ -384,12 +384,19 @@ format.POSIXlt <- function(x, format = "", usetz = FALSE,
     if(!inherits(x, "POSIXlt")) stop("wrong class")
     if(any(f0 <- format == "" | grepl("%OS$", format))) {
         ## need list [ method here.
-        times <- unlist(unclass(x)[1L:3L])[f0]
+    times <- unlist(unclass(x)[1L:3L])[f0]
+    secs <- x$sec[f0]; secs <- secs[is.finite(secs)]
         np <- if(is.null(digits)) 0L else min(6L, digits)
-        format[f0] <-
-            if(all(times[is.finite(times)] == 0)) "%Y-%m-%d"
-            else if(np == 0L) "%Y-%m-%d %H:%M:%S"
-            else paste0("%Y-%m-%d %H:%M:%OS", np)
+        if(np >= 1L) # no unnecessary trailing '0' :
+            for (i in seq_len(np)- 1L)
+                if(all( abs(secs - trunc(secs*10^i)/10^i) < 1e-6 )) {
+                    np <- i
+                    break
+                }
+    format[f0] <-
+        if(all(times[is.finite(times)] == 0)) "%Y-%m-%d"
+        else if(np == 0L) "%Y-%m-%d %H:%M:%S"
+        else paste0("%Y-%m-%d %H:%M:%OS", np)
     }
     .Internal(format.POSIXlt(x, format, usetz))
 }