D3.js dynamically switching using live data

Question

D3.js dynamically switching using live data

Long time lurker, learning D3 with enthusiasm! Anywhoo, I am working on Mr. Bostock's examples.

Now I have a fiddle that works just fine - it's smooth, refreshes fast, scales the x-axis and y-axis pretty well.

This is the timing diagram that I am trying to solve. Basically, I take sensor chains that come in a JSON array. My goal is to get this data in real time; The sensor sends the tempo, and I get a smooth reflection of this data on the graph in near real time. Here rub. Once I add the code to collect the JSON, things go from smooth as butter to choppy and crazy. This is what I'm working with ... Please understand that I am very new to D3.

Here is some nicely randomized code that displays the graph the way I want:

var n = 40,
    duration = 750,
    now = new Date(Date.now() - duration),
    random = d3.random.normal(0, 0.2),
    count = 0,
    data = d3.range(n).map(random);

var margin = {
    top: 20,
    right: 20,
    bottom: 20,
    left: 40
},
    width = 500 - margin.left - margin.right,
    height = 300 - margin.top - margin.bottom;

var x = d3.time.scale()
    .domain([now - (n - 2) * duration, now - duration])
    .range([0, width]);

var y = d3.scale.linear()
    .domain([0, d3.max(data)])
    .range([height, 0]);



var line = d3.svg.line()
    .interpolate("basis")
    .x(function (d, i) {
    return x(now - (n - 1 - i) * duration);
})
    .y(function (d, i) {
    return y(d);
});

var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

svg.append("defs").append("clipPath")
    .attr("id", "clip")
    .append("rect")
    .attr("width", width)
    .attr("height", height);

var axis = svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(x.axis = d3.svg.axis().scale(x).orient("bottom"));

var yAx = svg.append("g")
    .attr("class", "y axis")
    .call(y.axis = d3.svg.axis().scale(y).orient("left"));

var path = svg.append("g")
    .attr("clip-path", "url(#clip)")
    .append("path")
    .datum(data)
    .attr("class", "line");


var transition = d3.select({}).transition()
    .duration(750)
    .ease("linear");

tick();

function tick() {
    transition = transition.each(function () {

        // update the domains
        now = new Date();
        x.domain([now - (n - 2) * duration, now - duration]);
        y.domain([0, d3.max(data) + 10]);


        // push a new data point onto the back
        data.push(20 + Math.random() * 100);

        // redraw the line, and slide it to the left
        path.attr("d", line)
            .attr("transform", null);

        // slide the x-axis left, rescale the y-axis
        axis.call(x.axis);
        yAx.call(y.axis);

        // slide the line left
        path.transition()
            .attr("transform", "translate(" + x(now - (n - 1) * duration) + ")");

        // pop the old data point off the front
        data.shift();
    }).transition().each("start", tick);
}

svg {
    font: 10px sans-serif;
}
.line {
    fill: none;
    stroke: orange;
    stroke-width: 1.5px;
}
.axis path, .axis line {
    fill: none;
    stroke: #000;
    shape-rendering: crispEdges;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

Run code

Now I understand that my poor understanding of transitions is probably keeping me stuck. I need help with this! My problem starts when I add the following:

First, I add var JSONdata = [];

as global and then immediately after I function tick() { transition = transition.each(function () {

add the JSON code:

d3.json("tempdata.php", function(error, data){
    JSONdata = data;
    data.forEach(function(d) {
    JSONdata.temp = +d.temp;
})

I conclude by ending the end of the entire tick block with a final })

This is how it works ... but it's slow and choppy! There seem to be dragons in my crossings ...? I would like to have as much realtime time as possible, but even up to 5 seconds since buffered latency would be acceptable. Can anyone reach out a hand or some kind of enlightenment?

I would like the graph to display a constant line with the last updated value, so even if the gauge is disabled, I will see the last value. Ultimately, of course, I need to develop a circular approach to the type of database and actually solve the problem of better handling the timestamp. But it could be the next day.

My JSFiddle with only randomized data: http://jsfiddle.net/6z9qe46e/7/

+3

json dynamic transition d3.js linechart

SmokinGrunts Dec 23. 14 at 15:26

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