"Enhanced setDT Documentation: Added Example for RDS/RData Usage and FAQ Link" (#6894)

* faq updated

* updated example

* Update vignettes/datatable-faq.Rmd

Co-authored-by: Benjamin Schwendinger <[email protected]>

* final

* Update man/setDT.Rd

Co-authored-by: aitap <[email protected]>

* updated example

* style

* updated example

* example updated

* Update man/truelength.Rd

Co-authored-by: Benjamin Schwendinger <[email protected]>

* Update man/setDT.Rd

---------

Co-authored-by: Benjamin Schwendinger <[email protected]>
Co-authored-by: aitap <[email protected]>
Co-authored-by: Michael Chirico <[email protected]>

Author: 4 people

man/setDT.Rd

@@ -28,7 +28,8 @@ setDT(x, keep.rownames=FALSE, key=NULL, check.names=FALSE)
 }
 
 \seealso{
-  \code{\link{data.table}}, \code{\link{as.data.table}}, \code{\link{setDF}}, \code{\link{copy}}, \code{\link{setkey}}, \code{\link{setcolorder}}, \code{\link{setattr}}, \code{\link{setnames}}, \code{\link{set}}, \code{\link{:=}}, \code{\link{setorder}}
+  \code{\link{data.table}}, \code{\link{as.data.table}}, \code{\link{setDF}}, \code{\link{copy}}, \code{\link{setkey}}, \code{\link{setcolorder}}, \code{\link{setattr}}, \code{\link{setnames}}, \code{\link{set}}, \code{\link{:=}}, \code{\link{setorder}},
+  See the FAQ vignette: \code{vignette("datatable-faq", package = "data.table")}.
 }
 \examples{
 
@@ -58,6 +59,14 @@ setDT(X, key="a")[]
 X = list(a=1:5, a=6:10)
 setDT(X, check.names=TRUE)[]
 
+# Example demonstrating setDT after loading from RDS
+rds_file = tempfile(fileext = ".rds")
+X = data.table(a = 1:5, b = letters[1:5])
+saveRDS(X, rds_file)
+X_loaded = readRDS(rds_file)
+setDT(X_loaded)  # restore internal data.table attributes
+print(X_loaded)
+unlink(rds_file)
 }
 \keyword{ data }
 

vignettes/datatable-faq.Rmd

@@ -620,7 +620,10 @@ DT[ , b := rnorm(5)]  # 'replace' integer column with a numeric column
 
 ## Reading data.table from RDS or RData file
 
-`*.RDS` and `*.RData` are file types which can store in-memory R objects on disk efficiently. However, storing data.table into the binary file loses its column over-allocation. This isn't a big deal -- your data.table will be copied in memory on the next _by reference_ operation and throw a warning. Therefore it is recommended to call `setalloccol()` on each data.table loaded with `readRDS()` or `load()` calls.
+`*.RDS` and `*.RData` are file types which can store in-memory R objects on disk efficiently. However, storing `data.table` into a binary file loses its column over-allocation (see also `?truelength`). This isn't a big deal -- your `data.table` will be copied in memory on the next _by reference_ operation and throw a warning.  
+Therefore, it is recommended to call `setDT()` on each `data.table` loaded with `readRDS()` or `load()` calls to restore its internal attributes. If you only need to pre-allocate space for new columns, `setalloccol()` can also be used.  
+
+For more details, see `?setDT` and `?truelength`.
 
 # General questions about the package