Question

I am using d3 to make a stacked bar chart.

Thanks to this previous question I am binding data associated with a parent node to a child node using parentNode.__ data__.key.

The data is an array with one object for each bar (e.g ‘likes’). Then each object contains an array of values which drive the individual rectangles per bar:

data =  [{
          key = 'likes', values = [
            {key = 'blue-frog', value = 1}, 
            {key = 'goodbye', value = 2}
          ]
        }, {
          key = 'dislikes, values = [
            {key = 'blue-frog', value = 3},
            {key = 'goodbye', value = 4}
          ]
        }]

The chart is working fine, and so is binding the parent metric data to a child svg attribute:

// Create canvas
bars = svg.append("g");

// Create individual bars, and append data
// 'likes' are bound to first bar, 'dislikes' to second
bar = bars.selectAll(".bar")
        .data(data)        
        .enter()
        .append("g");

// Create rectangles per bar, and append data
// 'blue-frog' is bound to first rectangle, etc.
rect = bar.selectAll("rect")
        .data(function(d) { return d.values;})
        .enter()
        .append("rect");

// Append parent node information (e.g. 'likes') to each rectangle    
// per the SO question referenced above        
rect.attr("metric", function(d, i, j) {
  return rect[j].parentNode.__data__.key;
});

This then allows the creation of tooltips per rectangle which say things like “likes: 2.” So far so good.

The problem is how to associate this same information with a click event, building on:

rect.on("click", function(d) {
  return _this.onChartClick(d);
});

// or

rect.on("click", this.onChartClick.bind(this));

It’s problematic because the onChartClick method needs access to the bound data (d) and the chart execution context (‘this’). If it didn’t I could just switch the execution context and call d3.select(this).attr("metric") within the onChartClick method.

Another idea I had was to pass the metric as an additional parameter but the trick of using function(d, i, j) here doesn’t seem to work because it isn’t run until a click event happens.

Can you suggest a solution?

Answer 1

You could use the closure to keep a reference to the parent data like this:

bar.each(function(dbar) {            // dbar refers to the data bound to the bar
  d3.select(this).selectAll("rect")
      .on("click", function(drect) { // drect refers to the data bound to the rect
        console.log(dbar.key);       // dbar.key will be either 'likes' or 'dislikes'
      });
});

update:

See below for various ways to access different levels in your DOM structure. Mix and match! See the live version of this and try to click on the .rect divs: http://bl.ocks.org/4235050

var data =  [
    {
        key: 'likes',
        values: [{ key: 'blue-frog', value: 1 }, { key: 'goodbye', value: 2 }]
    }, 
    {
        key: 'dislikes',
        values: [{ key: 'blue-frog', value: 3 }, { key: 'goodbye', value: 4 }]
    }];

var chartdivs = d3.select("body").selectAll("div.chart")
    .data([data]) // if you want to make multiple charts: .data([data1, data2, data3])
  .enter().append("div")
    .attr("class", "chart")
    .style("width", "500px")
    .style("height", "400px");

chartdivs.call(chart); // chartdivs is a d3.selection of one or more chart divs. The function chart is responsible for creating the contents in those divs

function chart(selection) { // selection is one or more chart divs
  selection.each(function(d,i) { // for each chartdiv do the following
    var chartdiv = d3.select(this);
    var bar = chartdiv.selectAll(".bar")
        .data(d)
      .enter().append("div")
        .attr("class", "bar")
        .style("width", "100px")
        .style("height", "100px")
        .style("background-color", "red");  

    var rect = bar.selectAll(".rect")
        .data(function(d) { return d.values; })
      .enter().append("div")
        .attr("class", "rect")
        .text(function(d) { return d.key; })
        .style("background-color", "steelblue");

    bar.each(function(dbar) {
      var bardiv = d3.select(this);
      bardiv.selectAll(".rect")
          .on("click", function(drect) { 
            d3.select(this).call(onclickfunc, bardiv);
          });
    });

    function onclickfunc(rect, bar) { // has access to chart, bar, and rect
      chartdiv.style("background-color", bar.datum().key === 'likes' ? "green" : "grey");
      console.log(rect.datum().key); // will print either 'blue-frog' or 'goodbye'
    }
  });
}