Starting from version 1.14.2, data.table provides a robust mechanism for parameterizing expressions passed to the `i`, `j`, and `by` (or `keyby`) arguments of `[.data.table`. It is built upon the base R `substitute` function, and mimics its interface. Here, we introduce `substitute2` as a more robust and more user-friendly version of base R's `substitute`. For a complete list of differences between `base::substitute` and `data.table::substitute2` please read the [`substitute2` manual](https://rdatatable.gitlab.io/data.table/library/data.table/html/substitute2.html).

In the above example, we have seen a convenient feature of `substitute2`: automatic conversion from strings into names/symbols. An obvious question arises: what if we actually want to substitute a parameter with a *character* value, so as to have base R `substitute` behaviour. We provide a mechanism to escape automatic conversion by wrapping the elements into base R `I()` call. The `I` function marks an object as *AsIs*, preventing its arguments from substitution. (Read the `?AsIs` documentation for more details.) If base R behaviour is desired for the whole `env` argument, then it's best to wrap the whole argument in `I()`. Alternatively, each list element can be wrapped in `I()` individually. Let's explore both cases below.

In base R, splicing `cols` into a `list` can be achieved using `as.call(c(quote(list), cols))`. Additionally, starting from R 4.0.0, there is new interface for such an operation in the `bquote` function.