add examples to insert new column as first/last column (#5673)

* add examples to insert new column as first/last column
Co-authored-by: Benjamin Schwendinger <[email protected]>

Author: ben-schwen

NEWS.md

@@ -132,7 +132,7 @@
 
 23. `DT[, head(.SD,n), by=grp]` and `tail` are now optimized when `n>1`, [#5060](https://github.com/Rdatatable/data.table/issues/5060) [#523](https://github.com/Rdatatable/data.table/issues/523#issuecomment-162934391). `n==1` was already optimized. Thanks to Jan Gorecki and Michael Young for requesting, and Benjamin Schwendinger for the PR.
 
-24. `setcolorder()` gains `before=` and `after=`, [#4385](https://github.com/Rdatatable/data.table/issues/4358). Thanks to Matthias Gomolka for the request, and both Benjamin Schwendinger and Xianghui Dong for implementing.
+25. `setcolorder()` gains `before=` and `after=`, [#4385](https://github.com/Rdatatable/data.table/issues/4358). Thanks to Matthias Gomolka for the request, and both Benjamin Schwendinger and Xianghui Dong for implementing. Also thanks to Manuel López-Ibáñez for testing dev and mentioning needed documentation before release.
 
 25. `base::droplevels()` gains a fast method for `data.table`, [#647](https://github.com/Rdatatable/data.table/issues/647). Thanks to Steve Lianoglou for requesting, Boniface Kamgang and Martin Binder for testing, and Jan Gorecki and Benjamin Schwendinger for the PR. `fdroplevels()` for use on vectors has also been added.
 

man/setcolorder.Rd

@@ -34,6 +34,13 @@ setcolorder(DT, c("C", "A", "B"))
 
 #incomplete specification
 setcolorder(DT, "A")
+
+# insert new column as first column
+set(DT, j="D", value=sample(10))
+setcolorder(DT, "D", before=1)
+
+# move column to last column place
+setcolorder(DT, "A", after=ncol(DT))
 }
 \keyword{ data }