Histogram with tooltip in d3.js

Steps:

Classic pattern to add tooltip, as explained in the dedicated section.

But does not work very well, probably due to tiny bar size? Looks like the Y coordinate does not work very well.

TODO / work in progress / sorry for the inconvenience.

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

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>

<!-- Create a div where the graph will take place -->
<div id="my_dataviz"></div>

<script>

// set the dimensions and margins of the graph
var margin = {top: 10, right: 30, bottom: 30, left: 40},
    width = 460 - margin.left - margin.right,
    height = 400 - margin.top - margin.bottom;

// append the svg object to the body of the page
var svg = d3.select("#my_dataviz")
  .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 + ")");

// get the data
d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/1_OneNum.csv", function(data) {

  // X axis: scale and draw:
  var x = d3.scaleLinear()
      .domain([0, 1000])     // can use this instead of 1000 to have the max of data: d3.max(data, function(d) { return +d.price })
      .range([0, width]);
  svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

  // set the parameters for the histogram
  var histogram = d3.histogram()
      .value(function(d) { return d.price; })   // I need to give the vector of value
      .domain(x.domain())  // then the domain of the graphic
      .thresholds(x.ticks(70)); // then the numbers of bins

  // And apply this function to data to get the bins
  var bins = histogram(data);

  // Y axis: scale and draw:
  var y = d3.scaleLinear()
      .range([height, 0]);
      y.domain([0, d3.max(bins, function(d) { return d.length; })]);   // d3.hist has to be called before the Y axis obviously
  svg.append("g")
      .call(d3.axisLeft(y));

  // Add a tooltip div. Here I define the general feature of the tooltip: stuff that do not depend on the data point.
  // Its opacity is set to 0: we don't see it by default.
  var tooltip = d3.select("#my_dataviz")
    .append("div")
    .style("opacity", 0)
    .attr("class", "tooltip")
    .style("background-color", "black")
    .style("color", "white")
    .style("border-radius", "5px")
    .style("padding", "10px")

  // A function that change this tooltip when the user hover a point.
  // Its opacity is set to 1: we can now see it. Plus it set the text and position of tooltip depending on the datapoint (d)
  var showTooltip = function(d) {
    tooltip
      .transition()
      .duration(100)
      .style("opacity", 1)
    tooltip
      .html("Range: " + d.x0 + " - " + d.x1)
      .style("left", (d3.mouse(this)[0]+20) + "px")
      .style("top", (d3.mouse(this)[1]) + "px")
  }
  var moveTooltip = function(d) {
    tooltip
    .style("left", (d3.mouse(this)[0]+20) + "px")
    .style("top", (d3.mouse(this)[1]) + "px")
  }
  // A function that change this tooltip when the leaves a point: just need to set opacity to 0 again
  var hideTooltip = function(d) {
    tooltip
      .transition()
      .duration(100)
      .style("opacity", 0)
  }

  // append the bar rectangles to the svg element
  svg.selectAll("rect")
      .data(bins)
      .enter()
      .append("rect")
        .attr("x", 1)
        .attr("transform", function(d) { return "translate(" + x(d.x0) + "," + y(d.length) + ")"; })
        .attr("width", function(d) { return x(d.x1) - x(d.x0) -1 ; })
        .attr("height", function(d) { return height - y(d.length); })
        .style("fill", "#69b3a2")
        // Show tooltip on hover
        .on("mouseover", showTooltip )
        .on("mousemove", moveTooltip )
        .on("mouseleave", hideTooltip )

});
</script>

Steps:

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