faq updated

Author: venom1204

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)[]
 
+# FAQ: Dealing with data.table loaded from RDS or RData files
+# Example to demonstrate the usage of setDT after loading from RDS
+if (file.exists("my_data.rds")) {
+  X = readRDS("my_data.rds")  # Load data.table from RDS if file exists
+  setDT(X)  # Make sure to use setDT() after loading
+} else {
+  message("my_data.rds file does not exist. Skipping RDS loading example.")
+}
 }
 \keyword{ data }
 

man/truelength.Rd

@@ -44,7 +44,7 @@ alloc.col(DT,
     \code{setalloccol} \emph{reallocates} \code{DT} by reference. This may be useful for efficiency if you know you are about to going to add a lot of columns in a loop.
     It also returns the new \code{DT}, for convenience in compound queries.
 }
-\seealso{ \code{\link{copy}} }
+\seealso{ \code{\link{copy}}, See the FAQ vignette: \code{vignette("datatable-faq", package = "data.table")}.}
 \examples{
 DT = data.table(a=1:3,b=4:6)
 length(DT)                 # 2 column pointer slots used
@@ -54,5 +54,14 @@ length(DT)                 # 2 used
 truelength(DT)             # 2050 allocated, 2048 free
 DT[,c:=7L]                 # add new column by assigning to spare slot
 truelength(DT)-length(DT)  # 2047 slots spare
+
+# FAQ: Dealing with data.table loaded from RDS or RData files
+# Example to demonstrate the usage of setDT after loading from RDS
+if (file.exists("my_data.rds")) {
+  X = readRDS("my_data.rds")  # Load data.table from RDS if file exists
+  setDT(X)  # Make sure to use setDT() after loading
+} else {
+  message("my_data.rds file does not exist. Skipping RDS loading example.")
+}
 }
 \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 and `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