R: Modify elements conditionally

conditional-map {purrr}

R Documentation

Modify elements conditionally

Description

map_if() maps a function over the elements of .x satisfying a predicate. map_at() is similar but will modify the elements corresponding to a character vector of names or a mumeric vector of positions.

Usage

map_if(.x, .p, .f, ...)

map_at(.x, .at, .f, ...)

Arguments

`.x`	A list or atomic vector.
`.p`	A single predicate function, a formula describing such a predicate function, or a logical vector of the same length as `.x`. Alternatively, if the elements of `.x` are themselves lists of objects, a string indicating the name of a logical element in the inner lists. Only those elements where `.p` evaluates to `TRUE` will be modified.
`.f`	A function, formula, or atomic vector. If a function, it is used as is. If a formula, e.g. `~ .x + 2`, it is converted to a function with two arguments, `.x` or `.` and `.y`. This allows you to create very compact anonymous functions with up to two inputs. If character or integer vector, e.g. `"y"`, it is converted to an extractor function, `function(x) x[["y"]]`. To index deeply into a nested list, use multiple values; `c("x", "y")` is equivalent to `z[["x"]][["y"]]`. You can also set `.null` to set a default to use instead of `NULL` for absent components.
`...`	Additional arguments passed on to `.f`.
`.at`	A character vector of names or a numeric vector of positions. Only those elements corresponding to `.at` will be modified.

Value

A list.

Examples

# Convert factors to characters
iris %>%
  map_if(is.factor, as.character) %>%
  str()

# Specify which columns to map with a numeric vector of positions:
mtcars %>% map_at(c(1, 4, 5), as.character) %>% str()

# Or with a vector of names:
mtcars %>% map_at(c("cyl", "am"), as.character) %>% str()

list(x = rbernoulli(100), y = 1:100) %>%
  transpose() %>%
  map_if("x", ~ update_list(., y = ~ y * 100)) %>%
  transpose() %>%
  simplify_all()

[Package purrr version 0.2.2 Index]