Making a bar chart using d3.js

Question

My data is as follows:

var chartData = [[9.402974983096687, "Asian"], [10.762177012177013, "Black"], [12.213470319634704, "Chinese"], [11.211221431247658, "Hispanic"], [9.18421052631579, "American Indian"], [12.36144578313253, "Japanese"], [14.659334126040427, "Other"], [7.5, "Portuguese"], [10.636304446904095, "White"]];

I am trying to convert it to a format:

      [
{
    "Ethinicity": "Asian",
    "Facebook_usage": 9.40
},
{
    "Ethinicity" : "Black",
    "Freq": 12.213470319634704
},
{
    "Ethinicity":"Chinese"
    "Freq": 12.213470319634704
},

----]

Then, make a bar chart from this. Tried using a map function as follows:

chartData.map(function(e, i) {
  facebook_usage.push(e[0]);
  ethinicity.push(e[1]);
  }

var chartData = create_JSON(facebook_usage,ethinicity) {

    --not sure how to frame this function                 }

Here is the rest of the code to plot the bar chart:

    var margin = {top: 20, right: 20, bottom: 70, left: 40},
    width = 600 - margin.left - margin.right,
    height = 300 - margin.top - margin.bottom;


// set the ranges
var x = d3.scale.ordinal().rangeRoundBands([0, width], .05);

var y = d3.scale.linear().range([height, 0]);

// define the axis
var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")


var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .ticks(10);


// add the SVG element
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 + ")");


// load the data


    chartData.forEach(function(d) {
        d.ethinicity = d.ethinicity;
        d.facebook_usage = d.facebook_usage;
    });

  // scale the range of the data
  x.domain(data.map(function(d) { return d.ethinicity; }));
  y.domain([0, d3.max(data, function(d) { return d.facebook_usage; })]);

  // add axis
  svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis)
    .selectAll("text")
      .style("text-anchor", "end")
      .attr("dx", "-.8em")
      .attr("dy", "-.55em")
      .attr("transform", "rotate(-90)" );

  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 5)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Frequency");


  // Add bar chart
  svg.selectAll("bar")
      .data(chartData)
    .enter().append("rect")
      .attr("class", "bar")
      .attr("x", function(d) { return x(d.ethinicity); })
      .attr("width", x.rangeBand())
      .attr("y", function(d) { return y(d.facebook_usage); })
      .attr("height", function(d) { return height - y(d.facebook_usage); });

Still trying to find my way around d3.js. Below is the fiddle

Answer 1

There are several problems in your code right now.

1. You're using the variable data while setting your x and y domains. However that variable is not defined anywhere which is why the chart is not being generated.

2. You're defining 2 arrays and trying to do the data mapping twice. You can remove the first step. Doing the following is sufficient.

   // directly map your data  
   chartData.forEach(function(d) {
     d.ethinicity = d[1];
     d.facebook_usage = +d[0];
   });
   

Check the embedded snippet below.

P.S. your x-axis positioning is off, you will probably want to adjust it.

var chartData = [
  [9.402974983096687, "Asian"],
  [10.762177012177013, "Black"],
  [12.213470319634704, "Chinese"],
  [11.211221431247658, "Hispanic"],
  [9.18421052631579, "American Indian"],
  [12.36144578313253, "Japanese"],
  [14.659334126040427, "Other"],
  [7.5, "Portuguese"],
  [10.636304446904095, "White"]
];

// No need to do the below

/*
var facebook_usage = [];
var ethinicity = [];

chartData.map(function(e, i) {
      facebook_usage.push(e[0]);
      ethinicity.push(e[1]);
    });
    //console.log(chartData);
    */

var margin = {
    top: 20,
    right: 20,
    bottom: 70,
    left: 40
  },
  width = 600 - margin.left - margin.right,
  height = 300 - margin.top - margin.bottom;


// set the ranges
var x = d3.scale.ordinal().rangeRoundBands([0, width], .05);

var y = d3.scale.linear().range([height, 0]);

// define the axis
var xAxis = d3.svg.axis()
  .scale(x)
  .orient("bottom")


var yAxis = d3.svg.axis()
  .scale(y)
  .orient("left")
  .ticks(10);


// add the SVG element
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 + ")");


// load the data

// directly map your data here 
chartData.forEach(function(d) {
  d.ethinicity = d[1];
  d.facebook_usage = +d[0];
});

//console.log(chartData);

// scale the range of the data
x.domain(chartData.map(function(d) {
  return d.ethinicity;
}));
y.domain([0, d3.max(chartData, function(d) {
  return d.facebook_usage;
})]);

// add axis
svg.append("g")
  .attr("class", "x axis")
  .attr("transform", "translate(0," + height + ")")
  .call(xAxis)
  .selectAll("text")
  .style("text-anchor", "end")
  .attr("dx", "-.8em")
  .attr("dy", "-.55em")
  .attr("translate", "rotate(-90)");

svg.append("g")
  .attr("class", "y axis")
  .call(yAxis)
  .append("text")
  .attr("transform", "rotate(-90)")
  .attr("y", 5)
  .attr("dy", ".71em")
  .style("text-anchor", "end")
  .text("Frequency");


// Add bar chart
svg.selectAll("bar")
  .data(chartData)
  .enter().append("rect")
  .attr("class", "bar")
  .attr("x", function(d) {
    return x(d.ethinicity);
  })
  .attr("width", x.rangeBand())
  .attr("y", function(d) {
    return y(d.facebook_usage);
  })
  .attr("height", function(d) {
    return height - y(d.facebook_usage);
  });

.bar {
  fill: steelblue;
}

.bar:hover {
  fill: brown;
}

.axis {
  font: 10px sans-serif;
}

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

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>