D3 Tree Layout - Custom Vertical Layout when children exceed more than a certain number

Question

I'm trying to use the D3 Tree Layout to create a family tree of sorts and one of the things I noticed is that when I have many children nodes, it would stretch out horizontally across the screen. Ideally I would like a more vertical layout for these nodes so that people don't have to scroll across the screen and can just keep looking down the tree.

Here is what I currently see:

Now it might not be that bad, but if I had say 20 children, it would span across the whole screen and that is something I kind of want to avoid.

I have seen questions like this but this doesn't help me because I want a specific layout and not simply a resize... I have large nodes and they begin to collide with one another if I try to dynamically resize the tree -- shrinking the tree does not do me any good. I specifically need a different layout for situations where there are more than a certain number of children.

Here is kind of what I was envisioning/hoping for. Notice the root does not make this format because it has only 4 children. Ideally I want it so that if a parent has 5 or more children, it would result in the layout below. If the root had 5 children, it would result in this layout and the layout should simply stretch out vertically if users wanted to see the root's grandchildren (the A, B, C... nodes). If necessary I can get a diagram of that going:

I found a semi-similar question regarding custom children layouts and he said he had to play around with the actual d3js code. I kind of want to avoid this so I am hoping to find out if this is possible with d3js as it is right now and, if so, how to go about it? I don't need a complete answer, but a snippet of code proving that this is possible would be very helpful.

If necessary I can upload a JSFiddle for people to play around with.

Answer 1

Check out this fiddle:

http://jsfiddle.net/dyXzu/

I took the sample code from http://bl.ocks.org/mbostock/4339083 and made some modifications. Note that in the example, x and y are switched when drawing so the layout appears as a vertical tree.

The important thing I did was modifying the depth calculator:

Original:

// Normalize for fixed-depth.
nodes.forEach(function(d) { d.y = d.depth * 180; });

Fixed:

// Normalize for fixed-depth.
nodes.forEach(function (d) {
    d.y = d.depth * 180;
    if (d.parent != null) {
        d.x =  d.parent.x - (d.parent.children.length-1)*30/2
        + (d.parent.children.indexOf(d))*30;
    }
    // if the node has too many children, go in and fix their positions to two columns.
    if (d.children != null && d.children.length > 4) {
        d.children.forEach(function (d, i) {
            d.y = (d.depth * 180 + i % 2 * 100);
            d.x =  d.parent.x - (d.parent.children.length-1)*30/4
            + (d.parent.children.indexOf(d))*30/2 - i % 2 * 15;
        });
    }
});

Basically, I manually calculate the position of each node, overriding d3's default node positioning. Note that now there's no auto-scaling for x. You could probably figure this out manually by first going through and counting open nodes (d.children is not null if they exist, d._children stores the nodes when they are closed), and then adding up the total x.

Nodes with children in the two-column layout look a little funky, but changing the line-drawing method should improve things.