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.data and .env pronouns

Source: R/eval-tidy.R
dot-data.Rd

The .data and .env pronouns make it explicit where to find objects when programming with data-masked functions.

m <- 10
mtcars %>% mutate(disp = .data$disp * .env$m)

  • .data retrieves data-variables from the data frame.

  • .env retrieves env-variables from the environment.

Because the lookup is explicit, there is no ambiguity between both kinds of variables. Compare:

disp <- 10
mtcars %>% mutate(disp = .data$disp * .env$disp)
mtcars %>% mutate(disp = disp * disp)

Note that .data is only a pronoun, it is not a real data frame. This means that you can't take its names or map a function over the contents of .data. Similarly, .env is not an actual R environment. For instance, it doesn't have a parent and the subsetting operators behave differently.

.data versus the magrittr pronoun .

In a magrittr pipeline, .data is not necessarily interchangeable with the magrittr pronoun .. With grouped data frames in particular, .data represents the current group slice whereas the pronoun . represents the whole data frame. Always prefer using .data in data-masked context.

Where does .data live?

The .data pronoun is automatically created for you by data-masking functions using the tidy eval framework. You don't need to import rlang::.data or use library(rlang) to work with this pronoun.

However, the .data object exported from rlang is useful to import in your package namespace to avoid a R CMD check note when referring to objects from the data mask. R does not have any way of knowing about the presence or absence of .data in a particular scope so you need to import it explicitly or equivalently declare it with utils::globalVariables(".data").

Note that rlang::.data is a "fake" pronoun. Do not refer to rlang::.data with the rlang:: qualifier in data masking code. Use the unqualified .data symbol that is automatically put in scope by data-masking functions.