Apply head() across each element in a list of vectors

Apply head() across each element in a list of vectors

Usage

heads(x, n = 6, ...)

Arguments

x

list of atomic vectors, assumed to be the same atomic type.

n

integer maximum number of items to include from each element in the list x. When n contains multiple values, they are recycled to length(x) and applied to each list element in order.

...

additional arguments are passed to utils::head().

Value

list with at most n elements per vector.

Details

Note that this function currently only operates on a list of vectors. This function is notably faster than lapply(x, head, n) because it operates on the entire vector in one step.

Also the input n can be a vector so that each element in the list has a specific number of items returned.

See also

Other jam list functions: cPaste(), jam_rapply(), list2df(), mergeAllXY(), mixedSorts(), rbindList(), relist_named(), rlengths(), sclass(), sdim(), uniques(), unnestList()

Examples

l <- list(a=1:10, b=2:5, c=NULL, d=1:100);
heads(l, 1);
#> $a
#> [1] 1
#> 
#> $b
#> [1] 2
#> 
#> $c
#> integer(0)
#> 
#> $d
#> [1] 1
#> 

heads(l, 2);
#> $a
#> [1] 1 2
#> 
#> $b
#> [1] 2 3
#> 
#> $c
#> integer(0)
#> 
#> $d
#> [1] 1 2
#> 

heads(l, n=c(2, 1, 3, 5))
#> $a
#> [1] 1 2
#> 
#> $b
#> [1] 2
#> 
#> $c
#> integer(0)
#> 
#> $d
#> [1] 1 2 3 4 5
#>