Turning relationship data into hierarchical list in R

Question

This is my first question; so please, be gentle.

I have some data that is in the form of :

library('networkD3')
    Relationships<- data.frame(Parent=c("earth","earth","forest","forest","ocean","ocean","ocean","ocean"),
                  Child=c("ocean","forest","tree","sasquatch","fish","seaweed","mantis shrimp","sea monster"))
> Relationships
  Parent         Child
1  earth         ocean
2  earth        forest
3 forest          tree
4 forest     sasquatch
5  ocean          fish
6  ocean       seaweed
7  ocean mantis shrimp
8  ocean   sea monster

Essentially this is a list of edges that can be used to make a network map:

net <- graph_from_data_frame(d = Relationships,
                             directed = T)
plot(net)

I would like to convert it to a form that could be used in the diagonalNetwork function, below.

Hierarchical_list <- list(name = "earth",
                 children = list(list(name = "ocean",
                                      children = list(list(name = "mantis shrimp"),
                                                      list(name = "fish"),
                                                      list(name = "sea monster"),
                                                      list(name = "seaweed")
                                                      )),
                                 list(name = "forest",
                                      children = list(list(name = "sasquatch"),
                                                      list(name = "tree")
                                                      ))
                 ))
diagonalNetwork(Hierarchical_list)

Like this:

When I try to generate the list using this loop:

    List_attempt <- list()

levels<- levels(factor(Relationships$Parent))

for(n in 1:length(levels)){
  Children <- subset(Relationships, Relationships$Parent == levels[n], select = Child)
  for(c in 1:length(Children)){
    sublist <- as.list(Children)
    List_attempt <- list(List_attempt, name = levels[n],children = sublist)
  }
}

diagonalNetwork(List_attempt)

I get this error:

Error in FUN(X[[i]], ...) : 
  'options' must be a fully named list, or have no names (NULL)

1) Is there a better way of creating a list for diagonalNetwork?

2) Failing that; How can I modify my loops to kick out a list of the correct structure?

3) Is there a whole other function/package I should be using?

Thanks for any help you can give, I have been beating my head against this wall for a while. Feedback on better ways to ask questions on SO would also be welcomed.

Clarification:

A similar question is found here, Convert a data frame to a treeNetwork compatible list. However it relies on a data structure where the root is always in the first column, and its children are in subsequent columns, not a list of edges as in this question, which is commonly used in igraph.

Answer 1

thanks for pointing out the error @Symbolix

inspired by @MrFlick comment, suggestion to start from root and get child to create list elements recursively :) ... surely can be improved further for robustness against unexpected data inputs

library(igraph)
library('networkD3')
Relationships<- data.frame(Parent=c("earth","earth","forest","forest","ocean","ocean","ocean","ocean"),
    Child=c("ocean","forest","tree","sasquatch","fish","seaweed","mantis shrimp","sea monster"))
net <- graph_from_data_frame(d=Relationships, directed=T)
plot(net)

#net and Relationships as declared in question
#get root
root <- setdiff(Relationships$Parent, Relationships$Child)

#traverse next layer and then recurve
as.list.igraph <- function(thisNode) {
    nm <- vertex_attr(net, "name", thisNode)
    childNodes <- V(net)[which(shortest.paths(net, thisNode, mode="out") == 1)]
    if (length(childNodes)==0) return(list(name=nm))
    list(name=nm, children=unname(lapply(childNodes, as.list.igraph)))
}

#plot D3 network
diagonalNetwork(as.list.igraph(V(net)[root]))

btw, if I am not wrong, there is also a layout.reingold.tilford option in igraph