Modify a pluck location

• assign_in() takes a data structure and a pluck location, assigns a value there, and returns the modified data structure.

• modify_in() applies a function to a pluck location, assigns the result back to that location with assign_in(), and returns the modified data structure.

Usage

modify_in(.x, .where, .f, ...)

assign_in(x, where, value)

Arguments

.x, x

A vector or environment

.where, where

A pluck location, as a numeric vector of positions, a character vector of names, or a list combining both. The location must exist in the data structure.

.f

A function to apply at the pluck location given by .where.

...

Arguments passed to .f.

value

A value to replace in .x at the pluck location. Use zap() to instead remove the element.

See also

pluck()

Examples

# Recall that pluck() returns a component of a data structure that
# might be arbitrarily deep
x <- list(list(bar = 1, foo = 2))
pluck(x, 1, "foo")
#> [1] 2

# Use assign_in() to modify the pluck location:
str(assign_in(x, list(1, "foo"), 100))
#> List of 1
#>  $ :List of 2
#>   ..$ bar: num 1
#>   ..$ foo: num 100
# Or zap to remove it
str(assign_in(x, list(1, "foo"), zap()))
#> List of 1
#>  $ :List of 1
#>   ..$ bar: num 1

# Like pluck(), this works even when the element (or its parents) don't exist
pluck(x, 1, "baz")
#> NULL
str(assign_in(x, list(2, "baz"), 100))
#> List of 2
#>  $ :List of 2
#>   ..$ bar: num 1
#>   ..$ foo: num 2
#>  $ :List of 1
#>   ..$ baz: num 100

# modify_in() applies a function to that location and update the
# element in place:
modify_in(x, list(1, "foo"), \(x) x * 200)
#> [[1]]
#> [[1]]$bar
#> [1] 1
#> 
#> [[1]]$foo
#> [1] 400
#> 
#> 

# Additional arguments are passed to the function in the ordinary way:
modify_in(x, list(1, "foo"), `+`, 100)
#> [[1]]
#> [[1]]$bar
#> [1] 1
#> 
#> [[1]]$foo
#> [1] 102
#> 
#>