message on fread integer64 columns

NEWS.md

@@ -24,6 +24,8 @@
 
 3. Vignettes are now built using `litedown` instead of `knitr`, [#6394](https://github.com/Rdatatable/data.table/issues/6394). Thanks @jangorecki for the suggestion and @ben-schwen and @aitap for the implementation.
 
+4. `fread` now prints a message by default when creating one or more integer64 columns, warning that this type sometimes give unexpected results like in case of as.matrix(). The message can be suppressed with the new argument `no.integer64.message=TRUE`. To avoid integer64 columns, we can use options(datatable.integer64='numeric'). Thanks to @stefanfritsch, @mattdowle for the suggestion. [#3611](https://github.com/Rdatatable/data.table/issues/3611)
+
 ### BUG FIXES
 
 1. `fread()` with `skip=0` and `(header=TRUE|FALSE)` no longer skips the first row when it has fewer fields than subsequent rows, [#7463](https://github.com/Rdatatable/data.table/issues/7463). Thanks @emayerhofer for the report and @ben-schwen for the fix.

R/fread.R

@@ -7,7 +7,8 @@ showProgress=getOption("datatable.showProgress",interactive()), data.table=getOp
 nThread=getDTthreads(verbose), logical01=getOption("datatable.logical01",FALSE),
 logicalYN=getOption("datatable.logicalYN", FALSE),
 keepLeadingZeros=getOption("datatable.keepLeadingZeros",FALSE),
-yaml=FALSE, tmpdir=tempdir(), tz="UTC")
+yaml=FALSE, tmpdir=tempdir(), tz="UTC", no.integer64.message=FALSE
+)
 {
   if (missing(input)+is.null(file)+is.null(text)+is.null(cmd) < 3L) stopf("Used more than one of the arguments input=, file=, text= and cmd=.")
   input_has_vars = length(all.vars(substitute(input)))>0L  # see news for v1.11.6
@@ -261,13 +262,26 @@ yaml=FALSE, tmpdir=tempdir(), tz="UTC")
     if (identical(tt,"") || is_utc(tt)) # empty TZ env variable ("") means UTC in C library, unlike R; _unset_ TZ means local
       tz="UTC"
   }
+
   ans = .Call(CfreadR,input,identical(input,file),sep,dec,quote,header,nrows,skip,na.strings,strip.white,blank.lines.skip,comment.char,
               fill,showProgress,nThread,verbose,warnings2errors,logical01,logicalYN,select,drop,colClasses,integer64,encoding,keepLeadingZeros,tz=="UTC")
   if (!length(ans)) return(null.data.table())  # test 1743.308 drops all columns
   nr = length(ans[[1L]])
   require_bit64_if_needed(ans)
   setattr(ans,"row.names",.set_row_names(nr))
 
+  # integer64 message on create - instead of warning
+  if (!isTRUE(no.integer64.message) &&
+      identical(integer64, "integer64") &&
+      any(vapply(ans, inherits, logical(1L), what = "integer64"))) {
+    message(
+      "fread: Creating one or more integer64 columns. 
+      See ?fread and ?bit64::integer64.
+      To suppress this message, use no.integer64.message=TRUE.
+      To avoid integer64 columns, use options(datatable.integer64='numeric')."
+    )
+  }
+
   if (isTRUE(data.table)) {
     setattr(ans, "class", c("data.table", "data.frame"))
     setalloccol(ans)

inst/tests/tests.Rraw

@@ -21978,3 +21978,12 @@ local({
   test(2357.1, fread(f), DT)
   test(2357.2, fread(paste0("file://", f)), DT)
 })
+#3611 fread integer64 message
+test(2358.1,
+  suppressMessages(fread("a\n1\n2\n", colClasses = "integer64")),
+  data.table(a = as.integer64(c(1,2)))
+)
+test(2358.2,
+  suppressMessages(fread("a\n1\n2\n", colClasses = "integer64", no.integer64.message = TRUE)),
+  data.table(a = as.integer64(c(1,2)))
+)

man/fread.Rd

@@ -25,7 +25,8 @@ nThread=getDTthreads(verbose),
 logical01=getOption("datatable.logical01", FALSE),
 logicalYN=getOption("datatable.logicalYN", FALSE),
 keepLeadingZeros = getOption("datatable.keepLeadingZeros", FALSE),
-yaml=FALSE, tmpdir=tempdir(), tz="UTC"
+yaml=FALSE, tmpdir=tempdir(), tz="UTC",
+no.integer64.message=FALSE
 )
 }
 \arguments{