Develop Reference

d3.js How to create a separate element for each state in a country map?

I want to apply style to different states in a map of India: for now, a darker shade of some color based on certain data.
First I think I need to create a separate element for each state, and then set its fill color to a function of my data.
I'm really new to this. So this is probably quite easy to answer. I can't figure it out.
I tried to copy Bostock's code to create a separate path element for each country in the UK:
svg.selectAll(".subunit")
.data(topojson.feature(uk, uk.objects.subunits).features)
.enter().append("path")
.attr("class", function(d) { return "subunit " + d.id; })
.attr("d", path);
I have a geojson file called indiastates.geojson. The states appear to be labeled like so: "NAME_1": "Andaman and Nicobar".
What does the .data line need to say in my code? I keep getting errors that say topojson (or geojson, if I change topjson to geojson) is undefined.
I also wonder if this is doing almost the same thing?
var areas = group.append("path")
.attr("d", path)
.attr("class", "area")
.attr("stroke", "black")
.style("fill", "rgb(255, 102, 102)");

Sounds like what you want to do is create a "choropleth" map of the U.S. If you have a topojson states file, that's a good starting point, but it might need to be converted to CSV. Unfortunately, it's been 2+ years since I created a choropleth, and I did it in something other than D3js. Fortunately, there are a variety of tutorials. Just search in Google for "choropleth map for states in D3" (without the quotes)

Not able to get the Zoom/Pan and States name appear in India Map - D3?

I am new to D3.js. However after being practiced the examples of this site, I tried to play ahead with Mr.John Coogan's map given here. The output that I found in his site is as under
But when I am trying to do the same thing by placing his .js,css,.json and index.html in plunker it is coming as
Problems
a) No States are getting displayed
b) Zoom and Pan is not working
In another word, at this point of time I am looking only for the Indian map to work exactly as the example shown by Mr. Coogan.
What needs to be done for this?

Here's the working plunk: http://plnkr.co/1EqpIFecwJmkbvypTyQD?p=preview
You needed to uncomment this line:
.call(d3.behavior.zoom().on("zoom", redraw))
on line 40 of the index.html in your plunk, and then zoom and pan will work.
The state colors (based on wealth) are not showing because of various, more complex errors. The error shown in the console (svg is not defined referencing line 78) is just the start (you need to replace svg with india, which is defined).
In fact the whole original gist your example is based on is really just a work in progress, but most of the answers for how to fix it can be found in this thread from the google group, from Mike Bostock himself.
Essentially, the json data loads asynchronously, so need to be loaded in series.
// load the two JSON files in series
d3.json("states.json", function(states) {
d3.json("wealth.json", function(wealthdata) {
...
});
});
Then you can just apend the relevant colorbrewer CSS class when you first create each path:
india.selectAll("path")
.data(states.features)
.enter().append("path")
.attr("d", path)
.attr("class", function(d) {
return "q" + quantize(wealthdata[d.id]) + "-9";
})
.attr("d", path);
But you also need to define the quantize scale, range...:
var quantize = d3.scale.quantize()
.range(d3.range(9));
... and domain (which you can only do once the data has been loaded:
quantize.domain([0, d3.max(d3.values(wealthdata))]);

Drawing multiple sets of multiple lines on a d3.js chart

I have a d3 chart that displays two lines showing a country's imports and exports over time. It works fine, and uses the modular style described in 'Developing a D3.js Edge' so that I could quite easily draw multiple charts on the same page.
However, I now want to pass in data for two countries and draw imports and exports lines for both of them. After a day of experimentation, and getting closer to making it work, I can't figure out how to do this with what I have. I've successfully drawn multi-line charts with d3 before, but can't see how to get there from here.
You can view what I have here: http://bl.ocks.org/philgyford/af4933f298301df47854 (or the gist)
I realise there's a lot of code. I've marked with "Hello" the point in script.js where the lines are drawn. I can't work out how to draw those lines once for each country, as opposed to just for the first one, which is what it's doing now.
I'm guessing that where I'm applying data() isn't correct for this usage, but I'm stumped.
UPDATE: I've put a simpler version on jsfiddle: http://jsfiddle.net/philgyford/RCgaL/

The key to achieving what you want are nested selections. You first bind the entire data to the SVG element, then add a group for each group in the data (each country), and finally get the values for each line from the data bound to the group. In code, it looks like this (I've simplified the real code here):
var svg = d3.select(this)
.selectAll('svg')
.data([data]);
var g = svg.enter().append('svg').append('g');
var inner = g.selectAll("g.lines").data(function(d) { return d; });
inner.enter().append("g").attr("class", "lines");
inner.selectAll("path.line.imports").data(function(d) { return [d.values]; })
.enter().append("path").attr('class', 'line imports')
.attr("d", function(d) { return imports_line(d); });
The structure generated by this looks like svg > g > g.lines > path.line.imports. I've omitted the code for the export line here -- that would be below g.lines as well. Your data consists of a list of key-value pairs with a list as value. This is mirrored by the SVG structure -- each g.lines corresponds to a key-value pair and each path to the value list.
Complete demo here.

The point is that you're thinking to imperative. That's why you have so much code. I really can't put it better than Mike Bostock, you have to start Thinking with Joins:
svg.append("circle")
.attr("cx", d.x)
.attr("cy", d.y)
.attr("r", 2.5);
But that’s just a single circle, and you want many circles: one for each data point. Before you bust out a for loop and brute-force it, consider this mystifying sequence from one of D3’s examples.
Here data is an array of JSON objects with x and y properties, such as: [{"x": 1.0, "y": 1.1}, {"x": 2.0, "y": 2.5}, …].
svg.selectAll("circle")
.data(data)
.enter().append("circle")
.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; })
.attr("r", 2.5);
I'll leave translating this example to the "from one line to many lines" as an excerxise.

Updating a pie chart with a new data set with more values

I'm relatively new to D3 and have been following a few pie chart tutorials.
Namely the Mike Bostock Tutorials. http://bl.ocks.org/mbostock/1346410
But I have question about a donut chart updating from one data set to another with the 2nd data set having much more values than the first.
I have attempted this numerous times through an update function but no luck, I'll keep it simple and give a hypothetical example , lets say my first data set had 5 values
[1,2,3,4,5]
and my second data set had 10 values
[1,2,3,4,5,6,7,8,9,10]
only 5 values of the new data set would be depicted on the arcs after the dynamic update. It's like the pie is fixed with only 5 arc sections being able to display 5 values of the new dataset.
Any help would be appreciated as its been stumbling around with the idea for awhile!

The key to making it work with data of different size is to handle the .enter() and .exit() selections. This tutorial goes into more detail, but briefly the enter selection represents data for which no DOM elements exist (e.g. in the case where you pass in more data), the update selection (which you're already handling) represents data for which DOM elements exist and the exit selection DOM elements for which no data exists anymore (e.g. when you have more elements to start with).
So in your change function, you would need to do something like this.
function change() {
clearTimeout(timeout);
var path = svg.datum(data).selectAll("path")
.data(pie);
path.enter().append("path")
.attr("fill", function(d, i) { return color(i); })
.attr("d", arc)
.each(function(d) { this._current = d; }); // add the new arcs
path.transition().duration(750).attrTween("d", arcTween); // redraw the arcs
path.exit().remove(); // remove old arcs
}
This assumes that you're updating your data variable as you suggest above instead of getting a different value from the existing data structure as in the example.

Here I made a simple update that triggers when you click the text above the pie chart: JsFiddle
The main thing happening is all the data is updated when the .on("click") event triggers, so the chart gets updated like so:
d3.select("#update")
.on("click", function (d) {
data = [1,2,3,4,5,6,7,8,9,10];
vis.data([data]);
arc = d3.svg.arc().outerRadius(r);
pie = d3.layout.pie().value(function(d){return d; });
arcs.data(pie)
.enter()
.append("svg:g")
.attr("class", "slice")
.append("svg:path")
.attr("fill", function(d, i){return color(i);}).attr("d", arc);
});

d3: confusion about selectAll() when creating new elements

I am new to d3 and am using 'Interactive Data Visualization for the Web' by Scott Murray (which is great btw) to get me started. Now everything I saw so far works as described but something got me confused when looking at the procedure to create a new element. Simple example (from Scott Murray):
svg.selectAll("circle")
.data(dataset)
.enter()
.append("circle");
The name "circle" is used for the selectAll which returns an empty selection (which is ok as I learned). Then circles are appended by putting the same name into the .append. Great!
Now what got me confused was what happens when you want to do the same thing again. So you have a second dataset and want to generate new circles in the same way. Using the same code just replacing the dataset will obviously not work as the selectAll("circle") will not return an empty selection anymore. So I played around and found out that I can use any name in the selectAll and even leave it empty like this: selectAll()
Scott Murrays examples always just use one type (circle, text, etc.) per dataset. Finally I found in the official examples something like
svg.selectAll("line.left")
.data(dataset)
.enter()
.append("line")
.attr ...
svg.selectAll("line.right")
.data(dataset)
.enter()
.append("line");
.attr ...
Now my question: How is this entry in selectAll("ENTRY") really used? Can it be utilized later to again reference those elements in any way or is it really just a dummy name which can be chosen in any way and just needs to return an empty selection? I could not find this entry anywhere in the resulting DOM or object structure anymore.
Thank you for de-confusing me.

What you put in the selectAll() call before the call to .data() really only matters if you're changing/updating what's displayed. Imagine that you have a number of circles already and you want to change their positions. The coordinates are determined by the data, so initially you would do something like
svg.selectAll("circle")
.data(data)
.enter()
.append("circle")
.attr("cx", function(d) { return d; })
.attr("cy", function(d) { return d; });
Now your new data has the same number of elements, but different coordinates. To update the circle positions, all you need to do is
svg.selectAll("circle")
.data(newData)
.attr("cx", function(d) { return d; })
.attr("cy", function(d) { return d; });
What happens is that D3 matches the elements in newData to the existing circles (what you selected in selectAll). This way you don't need to append the circles again (they are there already after all), but only update their coordinates.
Note that in the first call, you didn't technically need to select circles. It is good practice to do so however just to make clear what you're trying to do and to avoid issues with accidentally selecting other elements.
You can find more on this update pattern here for example.