D3 choropleth map with legend - javascript

I have a choropleth map of the united states showing total population. I would like to add a legend to the map showing the quantile range values.I’ve seen other similar questions about this topic but can’t seem to get it to work for my specific case. I know I need to include the color range or color domain but just not sure if this is the correct way. As of right now just one feature shows up in the legend, could it be that all the legend features are stacked on top of each other. How can I know for sure and how can I fix this.
//Define default colorbrewer scheme
var colorSchemeSelect = "Greens";
var colorScheme = colorbrewer[colorSchemeSelect];
//define default number of quantiles
var quantiles = 5;
//Define quantile scale to sort data values into buckets of color
var color = d3.scale.quantile()
.range(colorScheme[quantiles]);
d3.csv(data, function (data) {
color.domain([
d3.min(data, function (d) {
return d.value;
}),
d3.max(data, function (d
return d.value
})
]);
//legend
var legend = svg.selectAll('rect')
.data(color.domain().reverse())
.enter()
.append('rect')
.attr("x", width - 780)
.attr("y", function(d, i) {
return i * 20;
})
.attr("width", 10)
.attr("height", 10)
.style("fill", color);

The legend code that you're using would work perfectly well if you had an ordinal scale, where the domain is made up of discrete values that correlate to the range of colours on a one-to-one basis. But you're using a quantile scale, and so need a different approach.
For a d3 quantile scale, the domain is the list of all possible input values, and the range is a list of discrete output values. The domain list is sorted in ascending order and then divided into equal-sized groups, which are assigned to each output value from the range. The number of groups is determined by the number of output values.
With that in mind, in order to get one legend entry for each colour, you're going to need to use your colour scale's range, not the domain, as the data for your legend. Then you can use the quantileScale.invertExtent() method to find the minimum and maximum input values that are getting drawn with that colour.
Sample code, making each legend entry a <g> containing both the coloured rectangle and a text label showing the corresponding values.
var legend = svg.selectAll('g.legendEntry')
.data(color.range().reverse())
.enter()
.append('g').attr('class', 'legendEntry');
legend
.append('rect')
.attr("x", width - 780)
.attr("y", function(d, i) {
return i * 20;
})
.attr("width", 10)
.attr("height", 10)
.style("stroke", "black")
.style("stroke-width", 1)
.style("fill", function(d){return d;});
//the data objects are the fill colors
legend
.append('text')
.attr("x", width - 765) //leave 5 pixel space after the <rect>
.attr("y", function(d, i) {
return i * 20;
})
.attr("dy", "0.8em") //place text one line *below* the x,y point
.text(function(d,i) {
var extent = color.invertExtent(d);
//extent will be a two-element array, format it however you want:
var format = d3.format("0.2f");
return format(+extent[0]) + " - " + format(+extent[1]);
});

Related

D3js legend color does not match to the map color javascript

I have a map already drawed. I would like to add a legend using d3.js. For example when filering by length, the map should show differents colors. Since a week, I couldn't achieve this task. My map color seem to be good but the legend does not match.
Could anybody help me with my draw link function ?
https://jsfiddle.net/aba2s/xbn9euh0/12/)
I think it's the error is about the legend function.
Here is the function that change my map color Roads.eachLayer(function (layer) {layer.setStyle({fillColor: colorscale(layer.feature.properties.length)})});
function drawLinkLegend(dataset, colorscale, min, max) {
// Show label
linkLabel.style.display = 'block'
var legendWidth = 100
legendMargin = 10
legendLength = document.getElementById('legend-links-container').offsetHeight - 2*legendMargin
legendIntervals = Object.keys(colorscale).length
legendScale = legendLength/legendIntervals
// Add legend
var legendSvg = d3.select('#legend-links-svg')
.append('g')
.attr("id", "linkLegendSvg");
var bars = legendSvg.selectAll(".bars")
//.data(d3.range(legendIntervals), function(d) { return d})
.data(dataset)
.enter().append("rect")
.attr("class", "bars")
.attr("x", 0)
.attr("y", function(d, i) { return legendMargin + legendScale * (legendIntervals - i-1); })
.attr("height", legendScale)
.attr("width", legendWidth-50)
.style("fill", function(d) { return colorscale(d) })
// create a scale and axis for the legend
var legendAxis = d3.scaleLinear()
.domain([min, max])
.range([legendLength, 0]);
legendSvg.append("g")
.attr("class", "legend axis")
.attr("transform", "translate(" + (legendWidth - 50) + ", " + legendMargin + ")")
.call(d3.axisRight().scale(legendAxis).ticks(10))
}
D3 expects your data array to represent the elements you are creating. It appears you are passing an array of all your features: but you want your scale to represent intervals. It looks like you have attempted this approach, but you haven't quite got it.
We want to access the minimum and maximum values that will be provided to the scale. To do so we can use scale.domain() which returns an array containing the extent of the domain, the min and max values.
We can then create a dataset that contains values between (and including) these two endpoints.
Lastly, we can calculate their required height based on how high the visual scale is supposed to be by dividing the height of the visual scale by the number of values/intervals.
Then we can supply this information to the enter/update/exit cycle. The enter/update/exit cycle expects one item in the data array for every element in the selection - hence why need to create a new dataset.
Something like the following shold work:
var dif = colorscale.domain()[1] - colorscale.domain()[0];
var intervals = d3.range(20).map(function(d,i) {
return dif * i / 20 + colorscale.domain()[0]
})
intervals.push(colorscale.domain()[1]);
var intervalHeight = legendLength / intervals.length;
var bars = legendSvg.selectAll(".bars")
.data(intervals)
.enter().append("rect")
.attr("class", "bars")
.attr("x", 0)
.attr("y", function(d, i) { return Math.round((intervals.length - 1 - i) * intervalHeight) + legendMargin; })
.attr("height", intervalHeight)
.attr("width", legendWidth-50)
.style("fill", function(d, i) { return colorscale(d) })
In troubleshooting your existing code, you can see you have too many elements in the DOM when representing the scale. Also, Object.keys(colorscale).length won't produce information useful for generating intervals - the keys of the scale are not dependent on the data.
eg

D3.js: Understanding Zoom in terms of svg

I have been looking into this d3.js block Timeline with Zoom. However, I am not able to figure out how the zoom function is actually implemented. Could somebody help me understand?
Frankly, there is no zoom happening.
var brush = d3.svg.brush()
.x(x)
.on("brush", display);//this calls display function on brush event drag.
Inside display function.
minExtent = brush.extent()[0],//this give the brush extent min
maxExtent = brush.extent()[1],//this give the brush extent max
Based on the max and min of the brush filter the data:
visItems = items.filter(function(d) {return d.start < maxExtent && d.end > minExtent;});
Reset the domain with the brush's max and min.
x1.domain([minExtent, maxExtent]);
Select all rectangles in the upper area not having the brush associate data to the DOM.
update it with the new scale values
rects = itemRects.selectAll("rect")
.data(visItems, function(d) { return d.id; })
.attr("x", function(d) {return x1(d.start);})
.attr("width", function(d) {return x1(d.end) - x1(d.start);});
create any new rectangles if the data is present but DOM is not present.
rects.enter().append("rect")
.attr("class", function(d) {return "miniItem" + d.lane;})
.attr("x", function(d) {return x1(d.start);})
.attr("y", function(d) {return y1(d.lane) + 10;})
.attr("width", function(d) {return x1(d.end) - x1(d.start);})
.attr("height", function(d) {return .8 * y1(1);});
Remove all the rectangle outsside the brush extent or not in the filtered item list visItems
rects.exit().remove();
Exactly the same for labels as done for rectangles above.
Hope this clears all your doubts.
I'm not sure but I think this is just a trick with D3 scales.
What happens is that it gets the selection below (which is a projection a 100% of with from time 0 to time 100) and plots into a new scale from time 50 to time 80 with the same width.
This will make the scale change in a way that looks like you zoomed on that time moment in time.

D3 brushing on grouped bar chart

I am trying to get brushing to work similar to this example, but with a grouped bar chart: http://bl.ocks.org/mbostock/1667367
I don't really have a good understanding of how brushing works (I haven't been able to find any good tutorials), so I'm a bit at a loss as to what is going wrong. I will try to include the relevant bits of code below. The chart is tracking the time to fix broken builds by day and then grouped by portfolio. So far the brush is created and the user can move and drag it, but the bars in the main chart are re-drawn oddly and the x axis is not updated at all. Any help you can give would be greatly appreciated. Thank you.
// x0 is the time scale on the X axis
var main_x0 = d3.scale.ordinal().rangeRoundBands([0, main_width-275], 0.2);
var mini_x0 = d3.scale.ordinal().rangeRoundBands([0, main_width-275], 0.2);
// x1 is the portfolio scale on the X axis
var main_x1 = d3.scale.ordinal();
var mini_x1 = d3.scale.ordinal();
// Define the X axis
var main_xAxis = d3.svg.axis()
.scale(main_x0)
.tickFormat(dateFormat)
.orient("bottom");
var mini_xAxis = d3.svg.axis()
.scale(mini_x0)
.tickFormat(dateFormat)
.orient("bottom");
After binding the data...
// define the axis domains
main_x0.domain(data.result.map( function(d) { return d.date; } )
.sort(d3.ascending));
mini_x0.domain(data.result.map( function(d) { return d.date; } )
.sort(d3.ascending));
main_x1.domain(data.result.map( function(d) { return d.portfolio; } )
.sort(d3.ascending))
.rangeRoundBands([0, main_x0.rangeBand() ], 0);
mini_x1.domain(data.result.map( function(d) { return d.portfolio; } )
.sort(d3.ascending))
.rangeRoundBands([0, main_x0.rangeBand() ], 0);
// Create brush for mini graph
var brush = d3.svg.brush()
.x(mini_x0)
.on("brush", brushed);
After adding the axis's, etc.
// Create the bars
var bar = main.selectAll(".bars")
.data(nested)
.enter().append("g")
.attr("class", function(d) { return d.key + "-group bar"; })
.attr("fill", function(d) { return color(d.key); } );
bar.selectAll("rect").append("rect")
.data(function(d) { return d.values; })
.enter().append("rect")
.attr("class", function(d) { return d.portfolio; })
.attr("transform", function(d) { return "translate(" + main_x0(d.date) + ",0)"; })
.attr("width", function(d) { return main_x1.rangeBand(); })
.attr("x", function(d) { return main_x1(d.portfolio); })
.attr("y", function(d) { return main_y(d.buildFixTime); })
.attr("height", function(d) { return main_height - main_y(d.buildFixTime); });
Here is the brush function (trying several different options)...
function brushed() {
main_x1.domain(brush.empty() ? mini_x1.domain() : brush.extent());
//main.select("rect")
//.attr("x", function(d) { return d.values; })
//.attr("width", function(d) { return d.values; });
bar.select("rect")
.attr("width", function(d) { return main_x1.rangeBand(); })
.attr("x", function(d) { return main_x1(d.portfolio); });
//.attr("y", function(d) { console.log(d); return main_y(d.buildFixTime); })
//.attr("height", function(d) { return main_height - main_y(d.buildFixTime); });
main.select(".x.axis").call(main_xAxis);
}
The problem comes from trying to use the brush to set the x-scale domain, when your x-scale is an ordinal scale. In other words, the expected domain of your x-axis is a list of categories, not a max-min numerical extent. So the problem is right at the top of the brushing function:
function brushed() {
main_x0.domain(brush.empty() ? mini_x0.domain() : brush.extent());
The domain set by brush.extent() is an array of two numbers, which then completely throws off your ordinal scale.
According to the wiki, if one of the scales attached to a brush function is an ordinal scale, the values returned by brush.extent() are values in the output range, not in the input domain. Ordinal scales don't have an invert() method to convert range values into domain values.
So, you have a few options on how to proceed:
You could re-do the whole graph using a linear time scale for your main x-axes instead of an ordinal scale. But then you have to write your own function to figure out the width of each day on that axis instead of being able to use .rangeBand().
You can create your own "invert" function to figure out which categorical values (dates on the mini_x0.domain) are included in the range returned by brush.extent(). Then you would have to both reset the main_x0.domain to only include those dates on the axis, and filter out your rectangles to only draw those rectangles.
Or you can leave the domain of main_x0. be, and change the range instead. By making the range of the graph larger, you space out the bars greater. In combination with a clipping path to cut off bars outside the plotting area, this has the effect of only showing a certain subset of bars, which is what you want anyway.
But what should the new range be? The range returned by brush.extent() is the beginning and end positions of the brushing rectangle. If you used these values as the range on the main graph, your entire graph would be squished down to just that width. That's the opposite of what you want. What you want is for the area of the graph that originally filled that width to be stretched to fill the entire plotting area.
So, if your original x range is from [0,100], and the brush covers the area [20,60], then you need a new range that satisfies these conditions:
the 20% mark of the new range width is at 0;
the 60% mark of the new range width is at 100.
Therefore,
the total width of the new range is ( (100-0) / (60-20) )*(100-0) = 250;
the start of the new range is at (0 - (20/100)*250) = -50;
the end of the new range is at (-50) + 250 = 200.
Now you could do all the algebra for figuring out this conversion yourself. But this is really just another type of scaling equation, so why not create a new scale function to convert between the old range and the zoomed-in range.
Specifically, we need a linear scale, with its output range set to be the actual range of the plotting area. Then set the domain according to the range of the brushed area that we want to stretch to cover the plotting area. Finally, we figure out the range of the ordinal scale by using the linear scale to figure out how far off the screen the original max and min values of the range would be. And from there, we-can resize the other ordinal scale and reposition all the rectangles.
In code:
//Initialization:
var main_xZoom = d3.scale.linear()
.range([0, main_width - 275])
.domain([0, main_width - 275]);
//Brushing function:
function brushed() {
var originalRange = main_xZoom.range();
main_xZoom.domain(brush.empty() ?
originalRange:
brush.extent() );
main_x0.rangeRoundBands( [
main_xZoom(originalRange[0]),
main_xZoom(originalRange[1])
], 0.2);
main_x1.rangeRoundBands([0, main_x0.rangeBand()], 0);
bar.selectAll("rect")
.attr("transform", function (d) {
return "translate(" + main_x0(d.date) + ",0)";
})
.attr("width", function (d) {
return main_x1.rangeBand();
})
.attr("x", function (d) {
return main_x1(d.portfolio);
});
main.select("g.x.axis").call(main_xAxis);
}
Working fiddle based on your simplified code (Note: you still need to set a clipping rectangle on the main plot):
http://fiddle.jshell.net/CjaD3/1/

D3 - Pie Chart & Force Directed Labels

I'm looking to create a pie chart with floating labels using D3. I'm new to D3 and I'm not even sure this is possible? Can you use the labels of one graph in another somehow? If you can, can you point me to an example?
Shorter Explanation:
I want labels from:
http://bl.ocks.org/1691430
...to be on a pie chart.
Here's the code I was running below:
Or in a JSBIN: http://jsbin.com/awilak/1/edit
If I understand his code correctly, this is the section that adds the labels. I don't understand what the labelForce.update does. From there, I don't care about transition, so that line isn't needed. Then the rest is just drawing the circles and adds a link / line? If someone could integrate that would be amazing but if you can help me understand what's going on and what I'm missing I'd be more than grateful.
// Now for the labels
// This is the only function call needed, the rest is just drawing the labels
anchors.call(labelForce.update)
labels = svg.selectAll(".labels")
.data(data, function(d,i) {return i;})
labels.exit()
.attr("class","exit")
.transition()
.delay(0)
.duration(500)
.style("opacity",0)
.remove();
// Draw the labelbox, caption and the link
newLabels = labels.enter().append("g").attr("class","labels")
newLabelBox = newLabels.append("g").attr("class","labelbox")
newLabelBox.append("circle").attr("r",11)
newLabelBox.append("text").attr("class","labeltext").attr("y",6)
newLabels.append("line").attr("class","link")
labelBox = svg.selectAll(".labels").selectAll(".labelbox")
links = svg.selectAll(".link")
labelBox.selectAll("text").text(function(d) { return d.num})
}
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
<title>Testing Pie Chart</title>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.js?2.1.3"></script>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.geom.js?2.1.3"></script>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.layout.js?2.1.3"></script>
<style type="text/css">
.slice text {
font-size: 16pt;
font-family: Arial;
}
</style>
</head>
<body>
<button id="button"> Test </button>
<br>
<form id="controls">
<div>
<h2>Y axis</h2>
<ul id="y-axis">
<li><label><input checked="checked" type="radio" name="y-axis" value="Component">Component</label></li>
<li><label><input type="radio" name="y-axis" value="Browser">Browser</label></li>
<li><label><input type="radio" name="y-axis" value="Version">Version</label></li>
</ul>
</div>
</form>
<script type="text/javascript">
// return a list of types which are currently selected
function plottableTypes () {
var types = [].map.call (document.querySelectorAll ("#coaster-types input:checked"), function (checkbox) { return checkbox.value;} );
return types;
}
var w = 600, //width
h = 600, //height
r = 100,
r2 = 200, //radius
axis = getAxis (), //axes
color = d3.scale.category20c(); //builtin range of colors
data = [
{"Browser":"Internet Explorer ","Version":"8.0","Toatl":2000,"Component":"6077447412293130422"},
{"Browser":"Internet Explorer ","Version":"9.0 ","Toatl":1852,"Component":"6077447412293130422"},
{"Browser":"Internet Explorer ","Version":"6.0 ","Toatl":1754,"Component":"6077447412293130422"},
{"Browser":"Firefox ","Version":"16.0 ","Toatl":1020,"Component":"6077447412293130422"},
{"Browser":"Chrome ","Version":"23.0 ","Toatl":972,"Component":"6077447412293130422"},
{"Browser":"Internet Explorer ","Version":"7.0 ","Toatl":700,"Component":"6077447412293130422"},
{"Browser":"Mobile Safari ","Version":"6.0 ","Toatl":632,"Component":"6077447412293130422"},
{"Browser":"BOT ","Version":"BOT ","Toatl":356,"Component":"6077447412293130422"},
{"Browser":"Firefox ","Version":"8.0 ","Toatl":196,"Component":"6077447412293130422"},
{"Browser":"Mobile Safari ","Version":"5.1 ","Toatl":184,"Component":"6077447412293130422"}
];
var vis = d3.select("body")
.append("svg:svg") //create the SVG element inside the <body>
.data([data]) //associate our data with the document
.attr("width", w) //set the width and height of our visualization (these will be attributes of the <svg> tag
.attr("height", h)
.append("svg:g") //make a group to hold our pie chart
.attr("transform", "translate(" + r2 + "," + r2 + ")") //move the center of the pie chart from 0, 0 to radius, radius
var arc = d3.svg.arc() //this will create <path> elements for us using arc data
.outerRadius(r);
var pie = d3.layout.pie() //this will create arc data for us given a list of values
.value(function(d) { return d.Toatl; }); //we must tell it out to access the value of each element in our data array
var arcs = vis.selectAll("g.slice") //this selects all <g> elements with class slice (there aren't any yet)
.data(pie) //associate the generated pie data (an array of arcs, each having startAngle, endAngle and value properties)
.enter() //this will create <g> elements for every "extra" data element that should be associated with a selection. The result is creating a <g> for every object in the data array
.append("svg:g") //create a group to hold each slice (we will have a <path> and a <text> element associated with each slice)
.attr("class", "slice"); //allow us to style things in the slices (like text)
arcs.append("svg:path")
.attr("fill", function(d, i) { return color(i); } ) //set the color for each slice to be chosen from the color function defined above
.attr("d", arc); //this creates the actual SVG path using the associated data (pie) with the arc drawing function
arcs.append("svg:text") //add a label to each slice
.attr("transform", function(d) { //set the label's origin to the center of the arc
//we have to make sure to set these before calling arc.centroid
d.innerRadius = r2;
d.outerRadius = r;
return "translate(" + arc.centroid(d) + ")"; //this gives us a pair of coordinates like [50, 50]
})
.attr("text-anchor", "middle") //center the text on it's origin
.text(function(d, i) {
if(axis.yAxis == "Component"){
return data[i].Component;
}
return data[i].Browser; //get the label from our original data array
});
d3.select('#button').on('click', reColor);
var arcOver = d3.svg.arc()
.outerRadius(r + 30)
.innerRadius(0);
var arc = d3.svg.arc()
.outerRadius(r)
.innerRadius(0);
var arcs = vis.selectAll("g.slice")
.attr("class", "slice")
.on("mouseover", function(d) {
getAxis();
d3.select(this)
.select("path")
.transition()
.duration(500)
.attr("d", arcOver);
d3.select(this).select("text")
.text(function(d, i) {
if(axis.yAxis == "Component"){
return data[i].Component;
}
return data[i].Browser; //get the label from our original data array
});
})
.on("mouseout", function(d) {
getAxis();
d3.select(this)
.select("path")
.transition()
.duration(500)
.attr("d", arc);
d3.select(this)
.select("text")
.text(function(d, i) {
if(axis.yAxis == "Component"){
return data[i].Component;
}
return data[i].Browser; //get the label from our original data array
});
});
function reColor(){
var slices = d3.select('body').selectAll('path');
slices.transition()
.duration(2000)
.attr("fill", function(d, i) { return color(i+2); } );
slices.transition()
.delay(2000)
.duration(2000)
.attr("fill", function(d, i) { return color(i+10); } )
}
function makeData(){
}
// return an object containing the currently selected axis choices
function getAxis () {
var y = document.querySelector("#y-axis input:checked").value;
return {
yAxis: y,
};
}
function update() {
axis = getAxis()
arcs.selectAll("text") //add a label to each slice
.text(function(d, i) {
if(axis.yAxis == "Component"){
return data[i].Component;
}
return data[i].Browser; //get the label from our original data array
});
}
document.getElementById("controls").addEventListener ("click", update, false);
document.getElementById("controls").addEventListener ("keyup", update, false);
</script>
</body>
</html>
As others mentioned in the comments to your introduction-post it's possible to achieve a solution like you described it and it's possible using your code plus parts of the "moving-labels"-example. If I understand you correctly, you want to achieve non-overlapping labels using the force-layout, which is a pretty nice idea that I didn't stumble upon yet.
The code-part you pasted from the example just draws the labels and the lines as you already explained correctly. The next step is to rearrange the labels in a force-like layout around your pie chart.
The part that rearranges the labels (and links) in the example is the following:
function redrawLabels() {
labelBox
.attr("transform",function(d) { return "translate("+d.labelPos.x+" "+d.labelPos.y+")"})
links
.attr("x1",function(d) { return d.anchorPos.x})
.attr("y1",function(d) { return d.anchorPos.y})
.attr("x2",function(d) { return d.labelPos.x})
.attr("y2",function(d) { return d.labelPos.y})
}
// Initialize the label-forces
labelForce = d3.force_labels()
.linkDistance(0.0)
.gravity(0)
.nodes([]).links([])
.charge(-60)
.on("tick",redrawLabels)
The function is the one that changes the positions of the labels and lines. The force is calculated by D3 and started with the d3.force_labels().... As you can see, the function is assigned as an event-handler for the tick-event. In other words: After every step of calculating the force, D3 calls the 'drawer' for every label and updates the positions.
Unfortunately I'm not very familiar with the force_labels() method of D3, but I would assume it works pretty much like the regular force().
An anchor, in your case, is placed somewhere in each pie-piece for each label. The more centered within each pie-piece (NOT the pie itself), the better. Unfortunately you have to calculate this anchor-position somehow (sin and cos stuff) and set the line-ends to this fixed position within redrawLabels().
After you've done this you will see the first result. You may have to play around with gravity, linkDistance etc values of the force to achieve good results. (That's what the silders in the example do.)
See d3 docs for more info: https://github.com/mbostock/d3/wiki/Force-Layout
Then you will maybe stumble upon the problem that the labels are ordered around the pie without overlapping but in some strange order. You could solve this by initially placing the labels in correct order on a larger circle around your pie instead of positioning them randomly around the panel, which is the cause for the problem. This way you will experience way less jitter and misplacements.
The idea also is described in another blocks example: http://bl.ocks.org/mbostock/7881887
In this example, the nodes are initially placed on a virtual circle. The positioning is calculated by the following functions:
x: Math.cos(i / m * 2 * Math.PI) * 200 + width / 2 + Math.random(),
y: Math.sin(i / m * 2 * Math.PI) * 200 + height / 2 + Math.random()
They represent a circle with a radius of 200, place in the center of the drawing-panel. The circle is divided into m equally large pieces. i/m just calculates the 'piece-positions' where i ranges from 0 to m-1.
Hope I could help!
Yes, you can definitely combine force-labels with a pie chart! There is nothing particularly special about the pie chart labels you started with, they're just text elements that can be positioned like anything else using transform or x/y. It looks like you were initially positioning these labels according to the centroids of the arcs they were labelling, but you can just as easily use another criteria (like the output of a force layout).
D3's force layout calculates positions for things based on a set of constraints about what is fixed, what is movable, and which are connected to which. The labelForce.update method from Mike's bl.ocks example is being used to inform the force layout about how many objects need to be positioned, and where the fixed "anchor" points are. It then saves the computed positions for the labels into the diagram's data model, and they are used later on in the redrawLabels function.
You need to create two arcs. One for the pie chart drawing, and one which is large for the labels to sit on.
// first arc used for drawing the pie chart
var arc = d3.svg.arc()
.outerRadius(radius - 10)
.innerRadius(0);
// label attached to first arc
g.append("text")
.attr("transform", function(d) { return "translate(" + arc.centroid(d) + ")"; })
.attr("dy", ".35em")
.style("text-anchor", "middle")
.text(function(d) { return d.data.age; });
// second arc for labels
var arc2 = d3.svg.arc()
.outerRadius(radius + 20)
.innerRadius(radius + 20);
// label attached to second arc
g.append("text")
.attr("transform", function(d) { return "translate(" + arc2.centroid(d) + ")"; })
.attr("dy", ".35em")
.style("text-anchor", "middle")
.text(function(d) { return d.data.age; });

D3 - how to deal with JSON data structures?

I'm new to D3, and spent already a few hours to find out anything about dealing with structured data, but without positive result.
I want to create a bar chart using data structure below.
Bars are drawn (horizontally), but only for user "jim".
var data = [{"user":"jim","scores":[40,20,30,24,18,40]},
{"user":"ray","scores":[24,20,30,41,12,34]}];
var chart = d3.select("div#charts").append("svg")
.data(data)
.attr("class","chart")
.attr("width",800)
.attr("height",350);
chart.selectAll("rect")
.data(function(d){return d3.values(d.scores);})
.enter().append("rect")
.attr("y", function(d,i){return i * 20;})
.attr("width",function(d){return d;})
.attr("height", 20);
Could anyone point what I did wrong?
When you join data to a selection via selection.data, the number of elements in your data array should match the number of elements in the selection. Your data array has two elements (for Jim and Ray), but the selection you are binding it to only has one SVG element. Are you trying to create multiple SVG elements, or put the score rects for both Jim and Ray in the same SVG element?
If you want to bind both data elements to the singular SVG element, you can wrap the data in another array:
var chart = d3.select("#charts").append("svg")
.data([data])
.attr("class", "chart")
…
Alternatively, use selection.datum, which binds data directly without computing a join:
var chart = d3.select("#charts").append("svg")
.datum(data)
.attr("class", "chart")
…
If you want to create multiple SVG elements for each person, then you'll need a data-join:
var chart = d3.select("#charts").selectAll("svg")
.data(data)
.enter().append("svg")
.attr("class", "chart")
…
A second problem is that you shouldn't use d3.values with an array; that function is for extracting the values of an object. Assuming you wanted one SVG element per person (so, two in this example), then the data for the rect is simply that person's associated scores:
var rect = chart.selectAll("rect")
.data(function(d) { return d.scores; })
.enter().append("rect")
…
If you haven't already, I recommend reading these tutorials:
Thinking with Joins
Nested Selections
This may clarify the nested aspect, in addition to mbostock's fine answer.
Your data has 2 degrees of nesting. You have an array of 2 objects, each has an array of ints. If you want your final image to reflect these differences, you need to do a join for each.
Here's one solution: Each user is represented by a group g element, with each score represented by a rect. You can do this a couple of ways: Either use datum on the svg, then an identity function on each g, or you can directly join the data on the g. Using data on the g is more typical, but here are both ways:
Using datum on the svg:
var chart = d3.select('body').append('svg')
.datum(data) // <---- datum
.attr('width',800)
.attr('height',350)
.selectAll('g')
.data(function(d){ return d; }) // <----- identity function
.enter().append('g')
.attr('class', function(d) { return d.user; })
.attr('transform', function(d, i) { return 'translate(0, ' + i * 140 + ')'; })
.selectAll('rect')
.data(function(d) { return d.scores; })
.enter().append('rect')
.attr('y', function(d, i) { return i * 20; })
.attr('width', function(d) { return d; })
.attr('height', 20);
Using data on the group (g) element:
var chart = d3.select('body').append('svg')
.attr('width',800)
.attr('height',350)
.selectAll('g')
.data(data) // <--- attach directly to the g
.enter().append('g')
.attr('class', function(d) { return d.user; })
.attr('transform', function(d, i) { return 'translate(0, ' + i * 140 + ')'; })
.selectAll('rect')
.data(function(d) { return d.scores; })
.enter().append('rect')
.attr('y', function(d, i) { return i * 20; })
.attr('width', function(d) { return d; })
.attr('height', 20);
Again, you don't have to create these g elements, but by doing so I can now represent the user scores differently (they have different y from the transform) and I can also give them different styles, like this:
.jim {
fill: red;
}
.ray {
fill: blue;
}

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