D3js PieChart will not perform UPDATE section - d3.js

Question

This is probably the simplest graph possible to create using d3js. And yet I am struggling.
The graph runs everything given to it in enter() and exit(). But everything in ENTER + UPDATE is completely ignored. WHY?
// Setup dimensions
var width = 200,
height = 200,
radius = Math.min(width, height) / 2,
// Setup a color function with 20 colors to use in the graph
color = d3.scale.category20(),
// Configure pie container
arc = d3.svg.arc().outerRadius(radius - 10).innerRadius(0), // Define the arc element
svg = d3.select(".pie").append("svg:svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")"),
// This is the layout manager for the pieGraph
pie = d3.layout.pie()
.sort(null)
.value(function (d) {
return d.answers;
}),
// Allow two groups in the container. One overlapping the other, just to make sure that
// text labels never get hidden below pie arcs.
graphGroup = svg.append("svg:g").attr("class", "graphGroup"),
textGroup = svg.append("svg:g").attr("class", "labelGroup");
// Data is loaded upon user interaction. On angular $scope update, refresh graph...
$scope.$watch('answers', function (data) {
// === DATA ENTER ===================
var g = graphGroup.selectAll("path.arc").data(pie(data)),
gEnter = g.enter()
.append("path")
.attr("d", arc)
.attr("class", "arc"),
t = textGroup.selectAll("text.label").data(data),
tEnter = t.enter()
.append("text")
.attr("class", "label")
.attr("dy", ".35em")
.style("text-anchor", "middle");
// === ENTER + UPDATE ================
g.select("path.arc")
.attr("id", function (d) {
return d.data.id + "_" + d.data.selection;
})
.attr("fill", function (d, i) {
return color(i);
})
.transition().duration(750).attrTween("d", function (d) {
var i = d3.interpolate(this._current, d);
this._current = i(0);
return function (t) {
return arc(i(t));
};
});
t.select("text.label")
.attr("transform", function (d) {
return "translate(" + arc.centroid(d) + ")";
})
.text(function (d) {
return d.data.opt;
});
// === EXIT ==========================
g.exit().remove();
t.exit().remove();
});
This one example of the json structure given to the update function as "data":
[{"selection":"0","opt":"1-2 timer","answers":"7"},
{"selection":"1","opt":"3-4 timer","answers":"13"},
{"selection":"2","opt":"5-6 timer","answers":"5"},
{"selection":"3","opt":"7-8 timer","answers":"8"},
{"selection":"4","opt":"9-10 timer","answers":"7"},
{"selection":"5","opt":"11 timer eller mer","answers":"11"},
{"selection":"255","opt":"Blank","answers":"8"}]

Answer 1

You don't need the additional .select() to access the update selection. This will in fact return empty selections in your case, which means that nothing happens. To make it work, simply get rid of the additional .select() and do
g.attr("id", function (d) {
return d.data.id + "_" + d.data.selection;
})
// etc
t.attr("transform", function (d) {
return "translate(" + arc.centroid(d) + ")";
})
// etc