Removing segments from a d3 animated pie - d3.js

Question

I have prototype code I am working with here:
jsfiddle
The example shows how to add a segment when new data is added but not how to remove it again when the data changes [back]. I am fairly new to d3 and don't quite get the exit() function yet...
if you reverse the initial and second dataset you will see that the grapes segment is never removed. Thanks in advance!
any help would be great!
The update code: (my final chart needs to update on a timer when data changes)
var arcs = arc_grp.selectAll("path")
.data(donut(data));
arcs.enter()
.append("path")
.attr("stroke", "white")
.attr("stroke-width", 0.8)
.attr("fill", function(d, i) { return color(i); })
.attr("d", arc)
.each(function(d) { return this.current = d; });
var sliceLabel = label_group.selectAll("text")
.data(donut(data));
sliceLabel.enter()
.append("text")
.attr("class", "arcLabel")
.attr("transform", function(d) { return "translate(" + (arc.centroid(d)) +
")"; })
.attr("text-anchor", "middle")
.style("fill-opacity", function(d) {
if (d.value === 0) { return 1e-6; }
else { return 1; }
})
.text(function(d) { return d.data.label; });
};

Answer 1

To remove elements without data, you have to use exit(), which...
Returns the exit selection: existing DOM elements in the selection for which no new datum was found.
So, inside your updateChart function, you need an exit selection for both paths and texts:
var newArcs = arcs.data(donut(dataset));
newArcs.exit().remove();
var newSlices = sliceLabel.data(donut(dataset));
newSlices.exit().remove();
Here is your updated code:
// Setup all the constants
var duration = 500;
var width = 500
var height = 300
var radius = Math.floor(Math.min(width / 2, height / 2) * 0.9);
var colors = ["#d62728", "#ff9900", "#004963", "#3497D3"];
// Test Data
var d2 = [{
label: 'apples',
value: 20
}, {
label: 'oranges',
value: 50
}, {
label: 'pears',
value: 100
}];
var d1 = [{
label: 'apples',
value: 100
}, {
label: 'oranges',
value: 20
}, {
label: 'pears',
value: 20
}, {
label: 'grapes',
value: 20
}];
// Set the initial data
var data = d1
var updateChart = function(dataset) {
var newArcs = arcs.data(donut(dataset));
newArcs.exit().remove();
newArcs.enter()
.append("path")
.attr("stroke", "white")
.attr("stroke-width", 0.8)
.attr("fill", function(d, i) {
return color(i);
})
.attr("d", arc);
newArcs.transition()
.duration(duration)
.attrTween("d", arcTween);
var newSlices = sliceLabel.data(donut(dataset));
newSlices.exit().remove();
newSlices.transition()
.duration(duration)
.attr("transform", function(d) {
return "translate(" + (arc.centroid(d)) + ")";
})
.style("fill-opacity", function(d) {
if (d.value === 0) {
return 1e-6;
} else {
return 1;
}
});
sliceLabel.data(donut(dataset)).enter()
.append("text")
.attr("class", "arcLabel")
.attr("transform", function(d) {
return "translate(" + (arc.centroid(d)) + ")";
})
.attr("text-anchor", "middle")
.style("fill-opacity", function(d) {
if (d.value === 0) {
return 1e-6;
} else {
return 1;
}
})
.text(function(d) {
return d.data.label;
});
};
var color = d3.scale.category20();
var donut = d3.layout.pie()
.sort(null)
.value(function(d) {
return d.value;
});
var arc = d3.svg.arc()
.innerRadius(radius * .4)
.outerRadius(radius);
var svg = d3.select("body")
.append("svg")
.attr("width", width)
.attr("height", height);
var arc_grp = svg.append("g")
.attr("class", "arcGrp")
.attr("transform", "translate(" + (width / 2) + "," + (height / 2) + ")");
var label_group = svg.append("g")
.attr("class", "lblGroup")
.attr("transform", "translate(" + (width / 2) + "," + (height / 2) + ")");
var arcs = arc_grp.selectAll("path")
.data(donut(data));
arcs.enter()
.append("path")
.attr("stroke", "white")
.attr("stroke-width", 0.8)
.attr("fill", function(d, i) {
return color(i);
})
.attr("d", arc)
.each(function(d) {
return this.current = d;
});
var sliceLabel = label_group.selectAll("text")
.data(donut(data));
sliceLabel.enter()
.append("text")
.attr("class", "arcLabel")
.attr("transform", function(d) {
return "translate(" + (arc.centroid(d)) + ")";
})
.attr("text-anchor", "middle")
.style("fill-opacity", function(d) {
if (d.value === 0) {
return 1e-6;
} else {
return 1;
}
})
.text(function(d) {
return d.data.label;
});
// Update the data
setInterval(function(model) {
return updateChart(d2);
}, 2000);
// Tween Function
var arcTween = function(a) {
var i = d3.interpolate(this.current, a);
this.current = i(0);
return function(t) {
return arc(i(t));
};
};
.arcLabel {
font: 10px sans-serif;
fill: #fff;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>