flatten() removes one level hierarchy from a list, while squash() removes all levels. These functions are similar to unlist() but they are type-stable so you always know what the type of the output is.

flatten(x)

flatten_lgl(x)

flatten_int(x)

flatten_dbl(x)

flatten_cpl(x)

flatten_chr(x)

flatten_raw(x)

squash(x)

squash_lgl(x)

squash_int(x)

squash_dbl(x)

squash_cpl(x)

squash_chr(x)

squash_raw(x)

flatten_if(x, predicate = is_spliced)

squash_if(x, predicate = is_spliced)

Arguments

x

A list of flatten or squash. The contents of the list can be anything for unsuffixed functions flatten() and squash() (as a list is returned), but the contents must match the type for the other functions.

predicate

A function of one argument returning whether it should be spliced.

Value

flatten() returns a list, flatten_lgl() a logical vector, flatten_int() an integer vector, flatten_dbl() a double vector, and flatten_chr() a character vector. Similarly for squash() and the typed variants (squash_lgl() etc).

Examples

x <- replicate(2, sample(4), simplify = FALSE) x
#> [[1]] #> [1] 1 3 2 4 #> #> [[2]] #> [1] 1 2 4 3 #>
flatten(x)
#> [[1]] #> [1] 1 3 2 4 #> #> [[2]] #> [1] 1 2 4 3 #>
flatten_int(x)
#> [1] 1 3 2 4 1 2 4 3
# With flatten(), only one level gets removed at a time: deep <- list(1, list(2, list(3))) flatten(deep)
#> [[1]] #> [1] 1 #> #> [[2]] #> [1] 2 #> #> [[3]] #> [[3]][[1]] #> [1] 3 #> #>
flatten(flatten(deep))
#> [[1]] #> [1] 1 #> #> [[2]] #> [1] 2 #> #> [[3]] #> [1] 3 #>
# But squash() removes all levels: squash(deep)
#> [[1]] #> [1] 1 #> #> [[2]] #> [1] 2 #> #> [[3]] #> [1] 3 #>
squash_dbl(deep)
#> [1] 1 2 3
# The typed flattens remove one level and coerce to an atomic # vector at the same time: flatten_dbl(list(1, list(2)))
#> [1] 1 2
# Only bare lists are flattened, but you can splice S3 lists # explicitly: foo <- set_attrs(list("bar"), class = "foo") str(flatten(list(1, foo, list(100))))
#> List of 3 #> $ : num 1 #> $ :List of 1 #> ..$ : chr "bar" #> ..- attr(*, "class")= chr "foo" #> $ : num 100
str(flatten(list(1, splice(foo), list(100))))
#> List of 3 #> $ : num 1 #> $ : chr "bar" #> $ : num 100
# Instead of splicing manually, flatten_if() and squash_if() let # you specify a predicate function: is_foo <- function(x) inherits(x, "foo") || is_bare_list(x) str(flatten_if(list(1, foo, list(100)), is_foo))
#> List of 3 #> $ : num 1 #> $ : chr "bar" #> $ : num 100
# squash_if() does the same with deep lists: deep_foo <- list(1, list(foo, list(foo, 100))) str(deep_foo)
#> List of 2 #> $ : num 1 #> $ :List of 2 #> ..$ :List of 1 #> .. ..$ : chr "bar" #> .. ..- attr(*, "class")= chr "foo" #> ..$ :List of 2 #> .. ..$ :List of 1 #> .. .. ..$ : chr "bar" #> .. .. ..- attr(*, "class")= chr "foo" #> .. ..$ : num 100
str(squash(deep_foo))
#> List of 4 #> $ : num 1 #> $ :List of 1 #> ..$ : chr "bar" #> ..- attr(*, "class")= chr "foo" #> $ :List of 1 #> ..$ : chr "bar" #> ..- attr(*, "class")= chr "foo" #> $ : num 100
str(squash_if(deep_foo, is_foo))
#> List of 4 #> $ : num 1 #> $ : chr "bar" #> $ : chr "bar" #> $ : num 100