update d3 pie chart with new data.json

Question

I have a dynamic data source that creates a new json in the browser frequently.

I was able to create a pie chart from this json using the code below (also at this fiddle)

var data=[{"crimeType":"mip","totalCrimes":24},{"crimeType":"theft","totalCrimes":558},{"crimeType":"drugs","totalCrimes":81},{"crimeType":"arson","totalCrimes":3},{"crimeType":"assault","totalCrimes":80},{"crimeType":"burglary","totalCrimes":49},{"crimeType":"disorderlyConduct","totalCrimes":63},{"crimeType":"mischief","totalCrimes":189},{"crimeType":"dui","totalCrimes":107},{"crimeType":"resistingArrest","totalCrimes":11},{"crimeType":"sexCrimes","totalCrimes":24},{"crimeType":"other","totalCrimes":58}];


var width = 800,
height = 250,
radius = Math.min(width, height) / 2;

var color = d3.scale.ordinal()
.range(["#98abc5", "#8a89a6", "#7b6888", "#6b486b", "#a05d56", "#d0743c", "#ff8c00"]);

var arc = d3.svg.arc()
.outerRadius(radius - 10)
.innerRadius(radius - 70);

var pie = d3.layout.pie()
.sort(null)
.value(function (d) {
return d.totalCrimes;
});



var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

var g = svg.selectAll(".arc")
    .data(pie(data))
    .enter().append("g")
    .attr("class", "arc");

g.append("path")
    .attr("d", arc)
    .style("fill", function (d) {
    return color(d.data.crimeType);
});

g.append("text")
    .attr("transform", function (d) {
    return "translate(" + arc.centroid(d) + ")";
})
    .attr("dy", ".35em")
    .style("text-anchor", "middle")
    .text(function (d) {
    return d.data.crimeType;
});

This data updates frequenty so what would be the best way to update the pie? Look at this fiddle. Here I have another json called data2.

How could I simply replace data with data2 and have the pie animate/update?

Note: on some updates values could == 0

Answer 1

I have created a working version and have posted it here: http://www.ninjaPixel.io/StackOverflow/doughnutTransition.html (for some reason I couldn't get the transitions to play ball in fiddle, so have just posted it to my website instead).

To make the code clearer I have omitted your labelling, renamed 'data' to 'data1', and have stuck in some radio buttons to flip between the data arrays. The following snippet shows the important bits. You can get the whole code from my page above.

var svg = d3.select("#chartDiv").append("svg")
    .attr("width", width)
    .attr("height", height)
    .append("g")
    .attr("id", "pieChart")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

var path = svg.selectAll("path")
    .data(pie(data1))
    .enter()
    .append("path");

  path.transition()
      .duration(500)
      .attr("fill", function(d, i) { return color(d.data.crimeType); })
      .attr("d", arc)
      .each(function(d) { this._current = d; }); // store the initial angles


function change(data){
    path.data(pie(data));
    path.transition().duration(750).attrTween("d", arcTween); // redraw the arcs

}

// Store the displayed angles in _current.
// Then, interpolate from _current to the new angles.
// During the transition, _current is updated in-place by d3.interpolate.
function arcTween(a) {
  var i = d3.interpolate(this._current, a);
  this._current = i(0);
  return function(t) {
    return arc(i(t));
  };
}

You may find this code of Mike Bostock's helpful, it is where I learned how to do this.