Using array inside JSON in D3 Graph

Question

Alright so I have a JSON that looks like this:

var anotherBlob = [
{
"daily_percentile_90th": 1159.8000000000002, 
"min_percentile_90th": 1159.8, 
"sparks": [
    3107.9, 
    2856.0, 
    2778.8, 
    2987.5, 
    3364.2, 
    3112.6, 
    2934.7, 
    2798.6, 
    2933.0, 
    2813.8, 
    2916.8, 
    2948.1, 
    2859.0, 
    1159.8
], 
"max_percentile_90th": 3364.2, 
"daily_percentile_50th": 804.0, 
"timerName": "Search:Books:SearchResults", 
"daily_average": 876.2513661202186
}, 
{
"daily_percentile_90th": 1598.8000000000002, 
"min_percentile_90th": 1598.8, 
"sparks": [
    4024.0, 
    3233.0, 
    3845.4, 
    3300.6, 
    4364.1, 
    4141.1, 
    4017.3, 
    4228.0, 
    4261.4, 
    5518.9, 
    5118.8, 
    4321.7, 
    4239.0, 
    1598.8
], 
"max_percentile_90th": 5518.9, 
"daily_percentile_50th": 1159.0, 
"timerName": "Temple:Shared", 
"daily_average": 1213.0819672131147
}, 
{
"daily_percentile_90th": 586.2, 
"min_percentile_90th": 586.2, 
"sparks": [
    15149.6, 
    15616.2, 
    15078.0, 
    15126.8, 
    15441.8, 
    15454.0, 
    12184.0, 
    11328.6, 
    13511.6, 
    11969.4, 
    12047.5, 
    11245.0, 
    14799.6, 
    11849.0
}];

And I am making a D3 graph based on the values in "sparks" - the problem is that I don't know how to iterate through the array because it is inside of a JSON. I can create a graph just fine based on any of the daily percentiles or averages, but I can't access the "sparks" data.

Here is what I have creating a graph based on the daily__percentile_90th and one based on the min_percentile_90th, but how should I change it to use the "sparks" data instead?

var daily90th = function(d) { return d.daily_percentile_90th }
var dailyMin = function(d) { return d.min_percentile_90th }
//These two lines go above the JSON in order to work.

(function() {
  var data = anotherBlob.slice()
  var x = d3.time.scale()
    .range([10, 280])
    .domain(d3.extent(data, dailyMin))

  var y = d3.scale.linear()
    .range([180, 10])
    .domain(d3.extent(data, daily90th))

  var svg = d3.select("#demo").append("svg:svg")
  .attr("width", 300)
  .attr("height", 200)
  svg.selectAll("circle").data(anotherBlob).enter()
   .append("svg:circle")
   .attr("r", 4)
   .attr("cx", function(d) { return x(dailyMin(d)) })
   .attr("cy", function(d) { return y(daily90th(d)) })
   .attr("style", "cursor: pointer;")
   .on("click", function(d) {
      d3.select("#demo .value").text("Timer Name: " + d.timerName)
   })
})();

Thank you. Any help will be much appreciated!

It sounds like you need nested selections here.

Lars Kotthoff
– Lars Kotthoff

2015-05-13 16:47:42 +00:00
Commented May 13, 2015 at 16:47 — Lars Kotthoff
– Lars Kotthoff, Commented May 13, 2015 at 16:47

JulCh · Accepted Answer · 2015-05-13 17:11:36Z

1

You can create another data selection in an existing data selection. As explained in the link given by Lars Kotthoff in comments, you have to do :

var dp90 = d3.selectAll("circle").data(data);
dp90.enter().append("g")... // Or "circle", "rect"... :)

This will create a selection with your global JSON.

Now, to access to "sparks" field, you can :

var sparks = dp90.selectAll(".spark").data(function(d){ return d.sparks });
sparks.enter().append("circle").attr("class", "spark")...

It will now iterate on each sparks array element, creating a circle for each one.

Hope it helps.

answered May 13, 2015 at 17:11

JulCh

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2 Comments

Eswizzle Over a year ago

Thank you so much for your answer, I really appreciate it! I guess I'm just too new to D3 to see how that would work though?

JulCh Over a year ago

Selection is a very difficult part to understand in d3js. Here, we associate each entry of 'data' (your global JSON) to a g element (for instance). That mean that g will now have a __data__ attribute containing object with "daily_percentile..., sparks, ...". You can now use this entry as a new selection data, a sub-selection, where you precise that new data entries come from d.sparks. Here is how data() works : github.com/mbostock/d3/wiki/Selections#data

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