Question

I created a multiple-line chart using nvd3, but was unable to modify it in some important ways. I would like to roll my own using straight d3js, but I’m struggling with thinking in joins.

I need to create a path for each d.key with its own corresponding d.values.

My data is formatted for nvd3 as follows (abridged).

[
    {
        "key":"brw-a",
        "values":[
            ["2012-07-11T00:00:00", 0.0 ],
            ["2012-07-11T23:59:59", 0.0 ],
            ["2012-07-05T06:31:47", 0.0 ],
            ["2012-07-05T23:59:59", 0.0 ]
        ]
    },
    {
        "key":"brw-c",
        "values":[
            ["2012-07-11T00:00:00", 0.0 ],
            ["2012-07-07T00:00:00", 2.0 ],
            ["2012-07-05T23:59:59", 4.0 ]
        ]
    }
]

I seem to need an inner loop to access the array stored in each d.values. I have a working example that demonstrates how d.values comes out in one big glob of uselessness.

var p = d3.select("body").selectAll("p")
        .data(data)
      .enter().append("p")
        .text(function(d) {return d.key +":  " + '[' + d.values + ']'})

I feel like I’m close, and it has something to do with:

.data(data, function(d) { return d.key; })

Update: I was able to manually loop over the data to create the desired effect. Perhaps there is not a way of doing this with joins? Save for using the wonderful nvd3 lib, of course. See the comment below for the link.

var body = d3.select("body")

for (i=0; i < data.length; i++) {
    var key = data[i].key
    var values = data[i].values

    body.append("h3")
        .text(key)

    for (j=0; j < values.length; j++) {
        body.append("p")
            .text(values[j][0] + " -- " + values[j][1])
    }

}

Answer 1

You were right about .data() function. But because you need to loop through elements in values, that’s what you need to pass as data for a nested selection:

.data(function(d) { return d.values})

You could try this:

var p = d3.select("body").selectAll("p")
        .data(data)
      .enter().append("p")
        .attr("id", function(d) { return d.key})
        .text(function(d) {return d.key})
            .selectAll("span")
                .data(function(d) { return d.values})
                .enter().append("span")
                    .text(function(d) {return d})

Produces:

<p id="brw-a">brw-a
    <span>2012-07-05T00:00:00,0</span>
    <span>2012-07-06T23:59:59,1</span>
    <span>2012-07-07T06:31:47,0</span>
    <span>2012-07-08T23:59:59,3</span>
</p>

<p id="brw-c">brw-c
    <span>2012-07-11T00:00:00,0</span>
    <span>2012-07-07T00:00:00,2</span>
    <span>2012-07-05T23:59:59,4</span>
</p>