Combine elements like `c` but preserving the attributes

patch-preserving-attributes-with-c.R

x <- structure(list(x = 1), "attr" = 2)
y <- structure(list(y = 3), "attr" = 1)
l <- list(x, y)
out <- do.call(c, l)

# doesn't quite work (notice the name)
out2 <- lapply(seq_along(out), function(i) {
  attributes(out[[i]]) <- attributes(l[[i]])
  out[[i]]
}) 
names(out2) <- names(out) # adding the names back
str(out2)
#> List of 2
#>  $ x: Named num 1
#>   ..- attr(*, "names")= chr "x"
#>   ..- attr(*, "attr")= num 2
#>  $ y: Named num 3
#>   ..- attr(*, "names")= chr "y"
#>   ..- attr(*, "attr")= num 1

# patchy solution
out <- do.call(c, l)
for(i in seq_along(out)) {
  attributes(out[[i]]) <- attributes(l[[i]])
}
str(out)
#> List of 2
#>  $ x: Named num 1
#>   ..- attr(*, "names")= chr "x"
#>   ..- attr(*, "attr")= num 2
#>  $ y: Named num 3
#>   ..- attr(*, "names")= chr "y"
#>   ..- attr(*, "attr")= num 1