UFO sightings - interactive line / scatter plot

This chart was created for a talk / workshop given at CodeHer Conference in Washington D.C. in 2017. You can find additional information and slides from the talk in this repository.

This scatter / line chart shows the ufo sightings count per month between 2000 and 2016. It includes the following interactions:

On hover, circle radius doubles and text appears showing the count associated with that data point. Additionally all other circles become more transparent when a circle is being hovered over. After hover, all circles go back to normal.
Upon clicking a year button, the chart will transition to display data from that particular year.

<!DOCTYPE html>
<meta charset="utf-8">

/*svg {
  border:1px solid #f0f;
}*/
.axis.y .tick {
  stroke-width:0.5px;
  stroke-dasharray: 2px 2px;
  stroke-opacity: .5;
}
.axis path {
  stroke: none;
}
.line {
  stroke: black;
  fill: none;
  stroke-width: 1.5;
}

.title {
  font: 20px sans-serif;
}

.line {
  stroke: darkgray;
  stroke-width: 3   ;
}

</style>

<body>

</body>
</body>

var radius = 10
var titleText = "UFO Sightings in "
var parseTime = d3.timeParse("%m/%Y");

//   Margin Conventions
var margin = {top: 40, right: 50, bottom: 30, left: 40};
var width = 900 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var svg = d3.select("body").append("svg")
  .attr("width", width + margin.left + margin.right)
  .attr("height", height + margin.top + margin.bottom)
  .append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

//   Define x and y scale
var xScale = d3.scaleTime()
  .range([0, width]);

var yScale = d3.scaleLinear()
  .domain([0, 1200])
  .range([height, 0]);

// Create x and y axis
var xAxis = d3.axisBottom(xScale)

var yAxis = d3.axisLeft(yScale)
  .tickSize(-width); //create gridlines

d3.csv("ufo.csv", ready)
  
function ready(error, data) {

if (error) return console.warn(error);

//   format data
  data.forEach(function(d) {
    d.date = parseTime(d.date);
    d.count = +d.count;
    d.year = d.date.getYear() + 1900
  });

window.data = data;
  
  // Function that allows for the swapping out of data in the plot
  function dataSwap(datasetYear) {

datasetYear = +datasetYear

thisDataGroup = data.filter(function(d) { return d.year == datasetYear})

xScale.domain(d3.extent(thisDataGroup, function(d) { return d.date; }));

svg.selectAll('.axis').filter('.x').call(xAxis)

svg.selectAll('.ufoGroup')
      .data(thisDataGroup)
      .transition()
      .attr('transform', function(d) { return 'translate(' + xScale(d.date) + ',' + yScale(d.count) + ')'})

svg.selectAll('.line')
      .transition()
      .attr('d', lineGenerator(thisDataGroup));

svg.select(".title")
      .text(titleText + datasetYear)
  }
  
//   create array of years for buttons
  years = d3.set(data.map(function(d) { return d.year })).values();

//   create buttons
  d3.select('.buttons')
    .selectAll('button')
    .data(years)
    .enter().append('button')
    .text(function(d) { return d})
    .on('click', function(d) {
      dataSwap(d)
    })
  
//   Define data we're starting with - just 2016 data
  var startData = data.filter(function(d) { return d.year == 2016;})

//   set domain of y scale
  yScale.domain(d3.extent(data, function(d) { return d.count; }));  
  xScale.domain(d3.extent(startData, function(d) { return d.date; }));

//   create color scale
  var colorScale = d3.scaleSequential(d3.interpolateCool)
    .domain([0, startData.length-1])

//   Add title text
  svg.append("text")
   .attr("class", "title")
   .attr("dy", -5)
   .text(titleText + startData[0].year)

//   Create x and y axis groups
  svg.append("g")
    .attr("class","x axis")
    .attr("transform","translate(0," + height + ")")
    .call(xAxis);

svg.append("g")
    .attr("class","y axis")
    .call(yAxis);
  
//   Create line 
  var lineGenerator = d3.line()
    .x(function(d) { return xScale(d.date)})
    .y(function(d) { return yScale(d.count)})
    .curve(d3.curveCardinal); //makes line 'curvy'

svg.append('path')
    .attr('class', 'line')
    .attr('d', lineGenerator(startData));

//   Create Group that will include circles and text
  var ufoGroup = svg.selectAll('.ufoGroup')
    .data(startData)
  .enter().append('g')
    .attr('class', 'ufoGroup')
    .attr('transform', function(d) { return 'translate(' + xScale(d.date) + ',' + yScale(d.count) + ')'})
    .on('mouseenter', function(d) {
//       append text to circle on hover
      d3.select(this)
        .append('text')
        .attr('dx', radius)
        .attr('dy', radius)
        .text(d.count)

//       make all circles lower opacity
      d3.selectAll('circle')
        .style('opacity', 0.5)

//       maintain full opacity only for circle currently moused over
      d3.select(this)
        .select('circle')
        .transition()
        .ease(d3.easeElastic)
        .duration(1000)
        .attr('r', radius*2)
        .style('opacity', 1)
    })
    .on('mouseleave', function(d) {

//       remove text on mouseleave
      d3.select(this)
        .select('text')
        .transition()
        .style('opacity', 0)
        .remove()
      
// put radius back to normal
      d3.select(this)
        .select('circle')
        .transition()
        .ease(d3.easeElastic)
        .duration(1000)
        .attr('r', radius)

//       opacity back to normal for all circles
      d3.selectAll('circle')
        .style('opacity', 1)
    });

//   append circle
  ufoGroup.append('circle')
    .attr('r', radius)
    .style('fill', function(d, i) { return colorScale(i); }); //to have color scale change across x data values (time)

}
</script>

https://d3js.org/d3.v4.min.js