Transitions with nested data D3.js - d3.js

Question

I've recently begun learning D3.js and I am struggling to create a transition in a scatter plot with the following data:
var data = [
{"year" : "2004", "x":100, "y":300, "size": 2, "type": "A"},
{"year" : "2005", "x":200, "y":200, "size": 2, "type": "A"},
{"year" : "2006", "x":300, "y":100, "size": 2, "type": "A"},
{"year" : "2004", "x":150, "y":250, "size": 2.382450, "type": "B"},
{"year" : "2005", "x":150, "y":250, "size": 3.078548, "type": "B"},
{"year" : "2006", "x":150, "y":250, "size": 4.265410, "type": "B"}];
Where in the scatter plot there are 2 points (type A&B) and they change location (x&y) and size by year. I've created a fiddle where I try to nest the data and plot the points, but making the next step of using transition() function is confusing. More specifically, I am still declaring the whole data, but to make transitions work I only need part of the data.

Answer 1

The key to understand what you want lies here:
There are 2 points and they change location (x&y) and size by year
Therefore, this is clearly a XY problem. Your problem is not "how to transition with nested data". Your problem is "how to transition by year".
My proposed solution involves, first of all, dropping that nested array. You don't need that.
Instead, get all the years in the data...
var years = [...new Set(data.map(function(d) {
return d.year
}))];
..., filter the data by year...
var dataStart = data.filter(function(d) {
return d.year === years[0]
});
... and loop trough the years. Here, I'm using d3.interval():
var counter = 1;
var timer = d3.interval(transition, 1500);
function transition() {
var newData = data.filter(function(d) {
return d.year === years[counter]
});
svg.selectAll("circle").data(newData)
.transition()
.duration(1000)
.attr("cx", function(d) {
console.log(d)
return d.x;
})
.attr("cy", function(d) {
return d.y;
})
.attr("r", function(d) {
return d.size * 10;
});
counter += 1;
if (counter === 3) {
timer.stop()
}
}
Here is the demo:
var data = [{
"year": "2004",
"x": 100,
"y": 100,
"size": 2,
"type": "A"
}, {
"year": "2005",
"x": 200,
"y": 180,
"size": 2,
"type": "A"
}, {
"year": "2006",
"x": 300,
"y": 50,
"size": 2,
"type": "A"
}, {
"year": "2004",
"x": 150,
"y": 150,
"size": 2.382450,
"type": "B"
}, {
"year": "2005",
"x": 150,
"y": 50,
"size": 3.078548,
"type": "B"
}, {
"year": "2006",
"x": 150,
"y": 100,
"size": 4.265410,
"type": "B"
}];
var width = 400,
height = 200;
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);
var years = [...new Set(data.map(function(d) {
return d.year
}))];
var dataStart = data.filter(function(d) {
return d.year === years[0]
});
var cell = svg.selectAll("circle")
.data(dataStart);
cell.enter()
.append("circle")
.attr("cx", function(d) {
return d.x;
})
.attr("cy", function(d) {
return d.y;
})
.attr("r", function(d) {
return d.size * 10;
});
var counter = 1;
var timer = d3.interval(transition, 1500);
function transition() {
var newData = data.filter(function(d) {
return d.year === years[counter]
});
svg.selectAll("circle").data(newData)
.transition()
.duration(1000)
.attr("cx", function(d) {
return d.x;
})
.attr("cy", function(d) {
return d.y;
})
.attr("r", function(d) {
return d.size * 10;
});
counter += 1;
if (counter === 3) {
timer.stop()
}
}
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