Replace data with new set - d3.js

Question

Using D3.js, I have something like this:
var sets = [
{ data:[{date:1980,value:10},{date:1981,value:20},{date:1982,value:30}] },
{ data:[{date:1981,value:10},{date:1982,value:20},{date:1983,value:30}] },
{ data:[{date:1982,value:10},{date:1983,value:20},{date:1984,value:30}] }
];
And I bind it to make a chart like this:
var paths = g.selectAll("path")
.data(sets);
paths.enter()
.append("path")
.datum(function(d) { return d.data; })
.attr("class","line")
.attr("d", line);
Where g is a g element inside an svg element. This works. For each item in set I get a path using the values in data. Now what I want to do is click an element and replace the data with a different set:
var altData = [
{ data:[{date:1980,value:30},{date:1981,value:20},{date:1982,value:10}] },
{ data:[{date:1981,value:10},{date:1982,value:20},{date:1983,value:30}] },
{ data:[{date:1982,value:10},{date:1983,value:20},{date:1984,value:0}] }
];
d3.select("#transition").on("click", function() {
paths.data(altData);
console.log("click");
});
But the paths.data(altData) doesn't appear to do anything. There are no console errors, but the chart doesn't change. What do I need to do to tell it that the data has changed and the lines should be redrawn? As a bonus, I'd really like this transition to be animated.
Full fiddle

Answer 1

Basically you need to tell d3 to redraw it. In your case, it is by calling attr("d", line).
For transition, put transition() between two attr("d", fnc). Your onclick function will look like the following
d3.select("#transition").on("click", function() {
paths.attr("d", line)
.transition()
.attr("d", function(d, i){
return line(altData[i].data)
})
});
Jsfiddle http://jsfiddle.net/8fLufc65/

Answer 2

Look at this plnkr that will change the data when transition is clicked.
I made the part that draws the lines into a function and pass the data for which it should be drawing the lines.
drawPaths(sets) ;
function drawPaths(sets) {
var g = svg.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
var paths = g.selectAll("path")
.data(sets);
paths.enter()
.append("path")
.datum(function(d) { console.log(d); return d.data; })
.attr("class","line")
.attr("d", line);
}