D3: use nest function to turn flat data with parent key into a hierarchy

Question

I\'m sure there\'s a really simple elegant way to do this but I can\'t quite figure it out. I have some input data that looks like this:

[
{id: 1, name: \"P         


        

Answer 1

You can't use the nest operator here because nesting produces a fixed hierarchy: the number of levels in the output hierarchy is the same as the number of key functions you specify.

That said, you can write your own function which produces a tree. Assuming that the root node is the first node in the input array, you can create a map from id to node, and then construct the tree lazily.

function tree(nodes) {
  var nodeById = {};

  // Index the nodes by id, in case they come out of order.
  nodes.forEach(function(d) {
    nodeById[d.id] = d;
  });

  // Lazily compute children.
  nodes.forEach(function(d) {
    if ("manager" in d) {
      var manager = nodeById[d.manager];
      if (manager.children) manager.children.push(d);
      else manager.children = [d];
    }
  });

  return nodes[0];
}

If you know that the nodes are listed in order such that managers appear before their reports, you can simplify the code to iterate only once.