Bar chart practice

My notes

Using Nathan's Hot Dog Contest datafile from flowingdata.com
Changing tsv to csv to read in datafile w/o modification

A variation of the example bar chart using a slightly more D.R.Y. style. The visual encoding is represented by two functions and their composition:

The value accessor returns the value (or property) to encode for a given data object.

The scale maps this value to a visual display encoding, such as a pixel position.

The map function represents the composition value ○ scale, mapping from data to display.

Inspired by Andrew Winterman’s post, Tooling for the Lazy Programmer: DRYing up D3.

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

body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.bar {
  fill: steelblue;
}

.x.axis path {
  display: none;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>

var margin = {top: 20, right: 20, bottom: 50, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var xValue = function(d) { return d.Year; }, // data -> value
    xScale = d3.scale.ordinal().rangeRoundBands([0, width], .1), // value -> display
    xMap = function(d) { return xScale(xValue(d)); }, // data -> display
    xAxis = d3.svg.axis().scale(xScale).orient("bottom");

var yValue = function(d) { return d.DogsEaten; }, // data -> value
    yScale = d3.scale.linear().range([height, 0]), // value -> display
    yMap = function(d) { return yScale(yValue(d)); }, // data -> display
    yAxis = d3.svg.axis().scale(yScale).orient("left");

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 + ")");

d3.csv("data.csv", type, function(error, data) {
  xScale.domain(data.map(xValue)); // data.map(xValue) returns an array of years
  yScale.domain([0, d3.max(data, yValue)]);

// Note: domain for ordinal needs to be the whole range, not just min/max

console.log ("data.map(xValue) = ", data.map(xValue));

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

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("x", margin.left + 20)
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Dogs Eaten");

svg.selectAll(".bar")
      .data(data)
    .enter().append("rect")
      .attr("class", "bar")
      .attr("x", xMap)
      .attr("width", xScale.rangeBand)
      .attr("y", yMap)
      .attr("height", function(d) { return height - yMap(d); })
      .attr("style", function(d) {if (d.NewRecord == 1) return "fill:green";})
      .attr("debug", function (d) {console.log(d); 
      console.log("x data = ", xValue(d)); 
      console.log("x pixel = ", xMap(d)); 
      console.log("y data = ", yValue(d)); 
      console.log("y pixel = ", yMap(d)); 
      console.log("width = ", xScale.rangeBand(d));
      });
});

function type(d) {
  d.DogsEaten = +d.DogsEaten;  // change string into number format
  return d;
}

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js