withDT: Use data.table syntax for one call
In moodymudskipper/withDT: Use data.table Syntax For One Call

Description Usage Arguments Details Examples

View source: R/withDT.R

Use data.table syntax for one call

1	withDT(expr, lock = getOption("withDT.lock"))

`expr`	an expression where `[` will forward its arguments to data.Table:::`[.data.table` if `x` inherits from data.frame
`lock`	wether to lock the intermediate data.table so syntax of assignment by reference is forbidden.

An important particularity of withDT() is that assignments are never done by reference. Though limiting it avoids the confusion and unintended behaviors that might come with them. The syntax of these assignments is still supported but will return a copy. In order to fail explicitly whenever that syntax is used, the argument lock can be set to TRUE.

Other benefits of this function are :

Leverage compact data.table syntax, and speed to a degree
Clearly isolate data.table code to avoid confusion due to hybrid syntax
Be sure that no data.table object is created in calling environment, avoiding potential confusion
Keep the class of x (regular data frame, tibble or other), with some exceptions detailed below

Some caveats are:

Copies are created for every call of [, which might be costly in some cases, if optimization is the goal we suggest using data.table::setDT() followed by idiomatic data.table syntax
Attributes other than class are stripped
Classes grouped_df and rowwise_df, created respectively by dplyr::group_by() and dplyr::rowwise() are stripped
When using syntax of assignment by reference and lock is FALSE (default), some expressions won't be equivalent to the data.table code, see examples However we think in these cases the behavior of withDT() is more likely to be expected

data.table is not attached so there is no risk of masking functions from other packages such as lubridate (11 conflicting functions), dplyr (4 conflicting functions) or purrr (1 conflicting function)

iris2 <- withDT(iris[, .(meanSW = mean(Sepal.Width)), by = Species][,cbind(.SD, a =3)])
iris2
class(iris2)
# can be also done as follows, which wouldn't have the same output with standard
# data.table code due to assignment by reference
iris3 <- withDT(iris[, .(meanSW = mean(Sepal.Width)), by = Species][,a:=3])
identical(iris2,iris3)
# iris wasn't modified
class(iris)
names(iris)
# but wouldn't work with lock == TRUE
try(iris4 <- withDT(lock=TRUE,iris[, .(meanSW = mean(Sepal.Width)), by = Species][,b:=3]))