Get an element from a nested list by path

Get an element from a nested list by path

Usage

list_get(x, path, default = NULL)

Arguments

x

A nested list to traverse.

Lists are traversed recursively. Non-list objects are treated as leaves. Data frames are not traversed and are treated as leaf values.

path

Character or integer vector giving the path to retrieve.

For a character path, each component selects a named element at the current level. For an integer path, each component selects an element by position. Positional indices are one-based, following normal R indexing conventions.

The path is evaluated from left to right. For example, c("b", "y", "i") means x[["b"]][["y"]][["i"]].

default

Value returned when the requested path does not exist or cannot be traversed.

The default is NULL.

Value

The value stored at path, or default if the path is missing or invalid.

See also

Other lstrrr_core: list_delete(), list_depth(), list_has(), list_nleaf(), list_path(), list_set()

Examples

x <- list(
  a = 1,
  b = list(
    x = 1,
    y = list(i = 1, j = 2)
  ),
  unnamed = list(10, 20),
  df = data.frame(z = 1:3)
)

list_get(x, c("b", "x"))
#> [1] 1
list_get(x, c("b", "y", "i"))
#> [1] 1

# Integer paths use positional indices
list_get(x, c(2L, 2L, 2L))
#> [1] 2

# Missing paths return `default`
list_get(x, c("b", "missing"), default = NA)
#> [1] NA

# Empty path returns the original object
list_get(x, character(0))
#> $a
#> [1] 1
#> 
#> $b
#> $b$x
#> [1] 1
#> 
#> $b$y
#> $b$y$i
#> [1] 1
#> 
#> $b$y$j
#> [1] 2
#> 
#> 
#> 
#> $unnamed
#> $unnamed[[1]]
#> [1] 10
#> 
#> $unnamed[[2]]
#> [1] 20
#> 
#> 
#> $df
#>   z
#> 1 1
#> 2 2
#> 3 3
#> 

# Data frames are treated as leaves
list_get(x, "df")
#>   z
#> 1 1
#> 2 2
#> 3 3
list_get(x, c("df", "z"), default = "not traversed")
#> [1] "not traversed"