apply several mouseover events to neighboring (connected) nodes

Question

I have a network diagram (force-directed graph), a scatterplot, and a table that are all interconnected (see jsFiddle). I have the interconnections working the way I want them for mouseover events. I would like to modify my code so that when I mouseover a node in the network diagram, not only is the moused-over node highlighted (and its connections in the scatterplot and table), but its immediate neighbor nodes are also highlighted (as well as their connections in the scatterplot and table).

I looked at the information in Highlight selected node, its links, and its children in a D3 force directed graph for help. Somewhere along the way (not exactly sure where) I found an example of a function that helps define the connected nodes, isConnected().

function isConnected(a, b) {
    return linkedByIndex[a.index + "," + b.index] || linkedByIndex[b.index + "," + a.index] || a.index == b.index;
    }

I'd like to incorporate this function into my mouseover events, perhaps with an if() statement, so that I can do all of the "highlighting" that I want. But, I'm new to D3 and js and am not sure how to set it up.

Below is the snippet of code (from the jsFiddle) that I would like to modify. I would appreciate any suggestions or pointers to other examples.

var node = svg.selectAll(".node")
    .data(graph.nodes)
    .enter().append("g")
    .attr("class", function(d) { return "node " + d.name + " " + d.location; })
    .call(force.drag)
    .on("mouseover", function(d) { 
        // I would like to insert an if statement to do all of these things to the connected nodes
        // if(isConnected(d, o)) {
            d3.select(this).select("circle").style("stroke-width", 6); 
            d3.select(this).select("circle").style("stroke", "orange"); 
            d3.select(this).select("text").style("font", "20px sans-serif");
            d3.selectAll("rect." + d.location).style("stroke-width", 6);
            d3.selectAll("rect." + d.location).style("stroke", "orange");
            d3.selectAll("text." + d.location).style("font", "20px sans-serif");
            d3.selectAll("tr." + d.name).style("background-color", "orange");
            //}
        })
    .on("mouseout",  function(d) { 
        // if(isConnected(d, o)) {
            d3.select(this).select("circle").style("stroke-width", 1.5); 
            d3.select(this).select("circle").style("stroke", "gray"); 
            d3.select(this).select("text").style("font", "12px sans-serif");
            d3.selectAll("rect." + d.location).style("stroke-width", 1.5);
            d3.selectAll("rect." + d.location).style("stroke", "gray");
            d3.selectAll("text." + d.location).style("font", "12px sans-serif");
            d3.selectAll("tr." + d.name).style("background-color", "white");
            //}
        });

Answer 1

In another scenario I would put my visual objects into a graph data structure and navigate that to efficiently update the appropriate items. But this is d3, but so we will do the same thing but instead of a graph data structure that we create we will use d3 selections (which can be like graphs but for this they will look a lot more like arrays). Algorithmically this approach will not be as efficient, but our graphs are small.

So working backwards I will want a selection that includes only the picked node's neighboring nodes. I will do this by selecting all the circles and then using the d3 selection filter method to reduce that to only those circles that are neighbors.

Of course then I need the list of neighbors, but a few nice js array methods make short work of that. The final relevant code (in mouseover) is not even that long - but I've added a bunch of comments:

// Figure out the neighboring node id's with brute strength because the graph is small
var nodeNeighbors = graph.links.filter(function(link) {
    // Filter the list of links to only those links that have our target 
    // node as a source or target
    return link.source.index === d.index || link.target.index === d.index;})
.map(function(link) {
    // Map the list of links to a simple array of the neighboring indices - this is
    // technically not required but makes the code below simpler because we can use         
    // indexOf instead of iterating and searching ourselves.
    return link.source.index === d.index ? link.target.index : link.source.index; });

// Reset all circles - we will do this in mouseout also
svg.selectAll('circle').style('stroke', 'gray');

// now we select the neighboring circles and apply whatever style we want. 
// Note that we could also filter a selection of links in this way if we want to 
// Highlight those as well
svg.selectAll('circle').filter(function(node) {
    // I filter the selection of all circles to only those that hold a node with an
    // index in my listg of neighbors
    return nodeNeighbors.indexOf(node.index) > -1;
})
.style('stroke', 'orange');

You can also try the fiddle

I think the important d3 concept relevant here is that when you associate data with an element (usually using the data() or datum() methods on selections) then that data sticks with that element and any future selections will always use it.

To link other aspects you can pull those attributes in a similar way and link them through d3. For example for the location rectangles you could add to mouseover:

var nodeLocations = graph.links.filter(function(link) {
        return link.source.index === d.index || link.target.index === d.index;})
    .map(function(link) {
        return link.source.index === d.index ? link.target.location : link.source.location; });

d3.selectAll("rect").filter(function(node) { return nodeLocations.indexOf(node.location) > -1; }) .style("stroke", "cyan");