rlang (version 0.1)

flatten: Flatten or squash a list of lists into a simpler vector

Description

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.

Usage

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

# NOT RUN {
x <- replicate(2, sample(4), simplify = FALSE)
x

flatten(x)
flatten_int(x)

# With flatten(), only one level gets removed at a time:
deep <- list(1, list(2, list(3)))
flatten(deep)
flatten(flatten(deep))

# But squash() removes all levels:
squash(deep)
squash_dbl(deep)

# The typed flattens remove one level and coerce to an atomic
# vector at the same time:
flatten_dbl(list(1, list(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))))
str(flatten(list(1, splice(foo), list(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))

# squash_if() does the same with deep lists:
deep_foo <- list(1, list(foo, list(foo, 100)))
str(deep_foo)

str(squash(deep_foo))
str(squash_if(deep_foo, is_foo))
# }