Extract name hierarchy for each leaf of a nested list

Question

I have an arbitrarily deep list that contains an arbitrary number of named character vectors. A simple example might be:

d <- c("foo", "bar")
names(d) <- c("d1", "d2")
e <- c("bar","foo")
names(e) <- c("d1", "d3")
l <- list(a1 = list(b1 = list(c1 = d, c2 = e), a2 = list(b1 = e)))
l

$a1
$a1$b1
$a1$b1$c1
  d1    d2 
"foo" "bar" 

$a1$b1$c2
  d1    d3 
"bar" "foo" 


$a1$a2
$a1$a2$b1
  d1    d3 
"bar" "foo" 

Id like to collect the (full) name at each leaf; for example,

collect_names(l)

"$a1$b1$c1" "$a1$b1$c2" "$a1$a2$b1"

A general solution that compares efficiency at the different "levels of arbitrary" gets extra credit ;)

Answer 1

wdots <- names(rapply(l,length))

This works for the example given, but I only found it thanks to @flodel's comment. If you want the dollar symbols, there's

wdols <- gsub('\\.','\\$',wdots)

though, as @thelatemail pointed out, this will not give you what you want if any of the names in your hierarchy contain "."

Answer 2

This recursive function seems to work:

collect_names <- function(l) {
  if (!is.list(l)) return(NULL)
  names <- Map(paste, names(l), lapply(l, collect_names), sep = "$")
  gsub("\\$$", "", unlist(names, use.names = FALSE))
}

collect_names(l)
# [1] "a1$b1$c1" "a1$b1$c2" "a1$a2$b1"

Answer 3

Other options:

Hierarchical view:

f <- function(x, parent=""){
    if(!is.list(x)) return(parent)
    mapply(f, x, paste(parent,names(x),sep="$"), SIMPLIFY=FALSE)
}

f(l)

$a1
$a1$b1
$a1$b1$c1
[1] "$a1$b1$c1"

$a1$b1$c2
[1] "$a1$b1$c2"


$a1$a2
$a1$a2$b1
[1] "$a1$a2$b1"

Just the names:

f <- function(x, parent=""){
    if(!is.list(x)) return(parent)
    unlist(mapply(f, x, paste(parent,names(x),sep="$"), SIMPLIFY=FALSE))
}

f(l)

   a1.b1.c1    a1.b1.c2    a1.a2.b1 
"$a1$b1$c1" "$a1$b1$c2" "$a1$a2$b1"