# Simple D3 demos

I've been playing with d3 recently, and it awesome! I'm especially amazed by the ease of animating transitions with it.

There are plenty of amazing d3 demos out there, but I wanted to write some simpler ones to help me understand the basics of d3. You can find them here:

For example, here's how to draw a circle with d3:

Code:

  var width = 200;
var height = 200;

var x = width/2;
var y = height/2;
var fill = '#F012BE';

var svg = d3.select("#d3-simple-circle").append("svg")
.attr("width", width)
.attr("height", height)
.append('circle')
.attr({ r: radius, cx: x, cy: y, fill: fill});


And here's one of the cooler-looking ones:

Code (granted, this one is a bit more complicated):

var width = 700;
var height = 500;

var linspace = function(start, stop, num_samples) {
return d3.range(start, stop * (num_samples / (stop-start)))
.map(function (n) { return n / (num_samples / (stop-start)); });
};

var direction = 1;
var x = linspace(0, 20, 500);
var y = x.map(function (i) { return ((height/2)-50) * direction * Math.sin(i); });

var x_step = width / x.length;
var y_middle = height / 2;

var fill = '#F012BE';

var sin_svg = d3.select("#dancing-sin-graph").append("svg")
.attr("width", width)
.attr("height", height);

sin_svg.selectAll('circle')
.data(y)
.enter()
.append('circle')
.attr({r: 2, fill: fill})
.attr('cx', function (d, i) {
return x_step * i;
})
.attr('cy', function (d, i) {
return y_middle - d;
});

function invert() {
direction = direction * -1;
y = x.map(function (i) { return ((height/2)-50) * direction * Math.sin(i); });

d3.select("#dancing-sin-graph").selectAll('circle')
.data(y)
.transition()
.duration(1000)
.attr({r: 2, fill: fill})
.attr('cx', function (d, i) {
return x_step * i;
})
.attr('cy', function (d, i) {
return y_middle - d;
});
}

// Make the interval just less than the transition duration so motion never stops
setInterval(invert, 900);