d3.legend example

README.md

d3.legend

d3.legend is a quick hack to add a legend to a d3 chart. Simply add a g and .call(d3.legend). Any elements that have a title set in the "data-legend" attribute will be included when d3.legend is called. Each title will appear only once (even when multiple items define the same data-legend) as the process uses a set based on a existing names, not an array of all items.

Color

By default the color in the legend will try to match the fill attribute or the stroke attribute of the relevant items. Color can be explicitly defined by attribute "data-legend-color"

Order

The order of items in the legend will be sorted using the top of the bounding box for each included item. The order can be explicitly defined by attribute "data-legend-pos"

Padding

Padding will be determined by attribute "data-style-padding" on the legend element. Defaults to 5.

Size

Size of the box is determined by font size, as items are placed using "em" and the frame around the items is based on the bounding box.

This Example

This example takes an existing Gist and adds a legend by defining data-legend for each series and calling d3.legend on a "g" element. To show the font-adjustment I change font-size after one second and call d3.legend again.

d3.legend

d3.legend is a quick hack to add a legend to a d3.graph. Simply add a g and .call(d3.legend). Any elements that has a title set in the "data-legend" attribute set will be included, when d3.legend is called. Each title will appear only once as the process uses a set based on a existing names, not an array of all items.

Color

By default the color in the legend will try to match the fill attribute or the stroke attribute of the relevant items. Color can be explicitly defined by attribute "data-legend-color"

Order

The order of items in the legend will be sorted using the top of the bounding box for each included item. The order can be explicitly defined by attribute "data-legend-pos"

Padding

Padding will be determined by attribute "data-style-padding" on the legend element. Defaults to 5.

Size

Size of the box is determined by font size, as items are placed using "em" and the frame around the items is based on the bounding box.

This Example

This example takes an existing Gist and adds a legend by defining data-legend for each series:

 .attr("data-legend",function(d) { return d.name})

Adding the legend is as simple as:

legend = svg.append("g")
  .attr("class","legend")
  .attr("transform","translate(50,30)")
  .style("font-size","12px")
  .call(d3.legend)

To show the font-adjustment I change font-size after one second and call d3.legend again.

##Comments on the original gist This line chart is constructed from a TSV file storing the daily average temperatures of New York, San Francisco and Austin over the last year. The chart employs conventional margins and a number of D3 features:

• d3.tsv - load and parse data
• d3.time.format - parse dates
• d3.time.scale - x-position encoding
• d3.scale.linear - y-position encoding
• d3.scale.category10, a d3.scale.ordinal - color encoding
• d3.extent, d3.min and d3.max - compute domains
• d3.keys - compute column names
• d3.svg.axis - display axes
• d3.svg.line - display line shape

d3.legend.js

// d3.legend.js 
// (C) 2012 [email protected]
// MIT licence

(function() {
d3.legend = function(g) {
  g.each(function() {
    var g= d3.select(this),
        items = {},
        svg = d3.select(g.property("nearestViewportElement")),
        legendPadding = g.attr("data-style-padding") || 5,
        lb = g.selectAll(".legend-box").data([true]),
        li = g.selectAll(".legend-items").data([true])

    lb.enter().append("rect").classed("legend-box",true)
    li.enter().append("g").classed("legend-items",true)

    svg.selectAll("[data-legend]").each(function() {
        var self = d3.select(this)
        items[self.attr("data-legend")] = {
          pos : self.attr("data-legend-pos") || this.getBBox().y,
          color : self.attr("data-legend-color") != undefined ? self.attr("data-legend-color") : self.style("fill") != 'none' ? self.style("fill") : self.style("stroke") 
        }
      })

    items = d3.entries(items).sort(function(a,b) { return a.value.pos-b.value.pos})

    
    li.selectAll("text")
        .data(items,function(d) { return d.key})
        .call(function(d) { d.enter().append("text")})
        .call(function(d) { d.exit().remove()})
        .attr("y",function(d,i) { return i+"em"})
        .attr("x","1em")
        .text(function(d) { ;return d.key})
    
    li.selectAll("circle")
        .data(items,function(d) { return d.key})
        .call(function(d) { d.enter().append("circle")})
        .call(function(d) { d.exit().remove()})
        .attr("cy",function(d,i) { return i-0.25+"em"})
        .attr("cx",0)
        .attr("r","0.4em")
        .style("fill",function(d) { console.log(d.value.color);return d.value.color})  
    
    // Reposition and resize the box
    var lbbox = li[0][0].getBBox()  
    lb.attr("x",(lbbox.x-legendPadding))
        .attr("y",(lbbox.y-legendPadding))
        .attr("height",(lbbox.height+2*legendPadding))
        .attr("width",(lbbox.width+2*legendPadding))
  })
  return g
}
})()

data.tsv

index.html

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

body {
  font: 10px sans-serif;
}

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

.x.axis path {
  display: none;
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

.legend rect {
  fill:white;
  stroke:black;
  opacity:0.8;}

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


var margin = {top: 20, right: 80, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y%m%d").parse;

var x = d3.time.scale()
    .range([0, width]);

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

var color = d3.scale.category10();

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

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

var line = d3.svg.line()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature); });

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.tsv("data.tsv", function(error, data) {
  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));

  data.forEach(function(d) {
    d.date = parseDate(d.date);
  });

  var cities = color.domain().map(function(name) {
    return {
      name: name,
      values: data.map(function(d) {
        return {date: d.date, temperature: +d[name]};
      })
    };
  });

  x.domain(d3.extent(data, function(d) { return d.date; }));

  y.domain([
    d3.min(cities, function(c) { return d3.min(c.values, function(v) { return v.temperature; }); }),
    d3.max(cities, function(c) { return d3.max(c.values, function(v) { return v.temperature; }); })
  ]);

  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("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Temperature (ºF)");

  var city = svg.selectAll(".city")
      .data(cities)
    .enter().append("g")
      .attr("class", "city");

  city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .attr("data-legend",function(d) { return d.name})
      .style("stroke", function(d) { return color(d.name); });

  city.append("text")
      .datum(function(d) { return {name: d.name, value: d.values[d.values.length - 1]}; })
      .attr("transform", function(d) { return "translate(" + x(d.value.date) + "," + y(d.value.temperature) + ")"; })
      .attr("x", 3)
      .attr("dy", ".35em")
      .text(function(d) { return d.name; });


  legend = svg.append("g")
    .attr("class","legend")
    .attr("transform","translate(50,30)")
    .style("font-size","12px")
    .call(d3.legend)

  setTimeout(function() { 
    legend
      .style("font-size","20px")
      .attr("data-style-padding",10)
      .call(d3.legend)
  },1000)

});

</script>

thumbnail.png

Very helpful and neat way of doing legend. Loved it. Noticed just one draw back. Can you implement the functionality to show different shapes in legend than just the circles? I have a map which displays different shapes using d3.svg.symbol().type. How can I get the legend to display what each type means. I appreciate your help.

I added an option to draw a line icon instead of a circle by setting the data-legend-icon attribute to line

See it here: http://bl.ocks.org/kielni/a4347fe16864903fb9be

Please use the index of the series selected to determine the each title. On rare occasions, multiple series may have the same name, and only one series may be rendered in the legend. Pretty simple fix.

svg.selectAll('[data-legend']).each(function (d, i) {
...
// items[self.attr('data-legend')] // overwrites matching series names
// use the index of the element found so all series' are accounted for
items[i] = { name: self.attr('data-legend'), ... }
...
});
...
li.selectAll('text')...text(function(d) {return d.value.name});
...

See: https://gist.github.com/wjaspers/0f85f8b2cf23c3f78129

I tried using d3.legend.js with d3 v4 but ran into a problem. So I ported index.html to use d3 v4 to see if the problem was in my code or in d3.legend.js. See https://gist.github.com/louking/6491d18c9cef56011971be76a85cde8e (http://bl.ocks.org/louking/6491d18c9cef56011971be76a85cde8e for running version) - the problem is at line 47 of d3.legend.js Uncaught TypeError: Cannot read property '0' of undefined.

I'm not that familiar with d3 (or the changes from v3) to understand this error -- any ideas?

Also posted at http://stackoverflow.com/questions/38774855/d3-legend-js-with-d3-v4 because it's not clear author is responding to comments here.

thanks

@louking, can you please share the latest version that works with D3 v4?

I believe this gist should become an actual project on GitHub, it is very useful from the screenshots.

Why you MIT guys are not able without germans write usable manuals? I follow all instructions and nothing happened.
var legenObj =[{name:"drugs"},{name:"no-drugs"}];

svg
.data(legenObj)
.enter()
.append("g")
.attr( "id","legend")
.attr("transform", "translate(20,20)")
.attr("data-legend",
(d=> d.name));

   legend = svg.append("g")
    .attr("class","legend")
    .attr("transform","translate(50,30)")
    .style("font-size","12px")
         .call(d3.legend)   ;