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I have some data. It looks like this (but with several hundred objects in the array rather than three):

var data = [
{
    id: "1",
    name: "Name1",
    color: "Color1"
},
{
    id: "2",
    name: "Name2",
    color: "Color2"
},
{
    id: "1",
    name: "Name3",
    color: "Color3"
}

What I want to do is draw a rectangle which has a height that corresponds to the number of items in the data which have a certain id value. So, for example, if there were 300 items in the data array with an id of "1", then the rectangle would be 300 pixels tall.

Obviously I could loop through the array and count them up, but I want to know if there's an easier/shorter way in d3.js.

What I have in mind might look like this:

svg.selectAll('rect').data(data).enter()
    .append('rect')
        .attr('x', 800)
        .attr('y', 800)
        .attr('height', //SOME CODE HERE)
        .attr('width', 5)
        .attr('fill', 'red')

I have some data. It looks like this (but with several hundred objects in the array rather than three):

var data = [
{
    id: "1",
    name: "Name1",
    color: "Color1"
},
{
    id: "2",
    name: "Name2",
    color: "Color2"
},
{
    id: "1",
    name: "Name3",
    color: "Color3"
}

What I want to do is draw a rectangle which has a height that corresponds to the number of items in the data which have a certain id value. So, for example, if there were 300 items in the data array with an id of "1", then the rectangle would be 300 pixels tall.

Obviously I could loop through the array and count them up, but I want to know if there's an easier/shorter way in d3.js.

What I have in mind might look like this:

svg.selectAll('rect').data(data).enter()
    .append('rect')
        .attr('x', 800)
        .attr('y', 800)
        .attr('height', //SOME CODE HERE)
        .attr('width', 5)
        .attr('fill', 'red')

• javascript
• d3.js
• data-visualization

Share Improve this question Follow edited May 26, 2014 at 6:48 ACPrice asked May 26, 2014 at 6:41 ACPriceACPrice 68722 gold badges1111 silver badges2525 bronze badges

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1 Answer 1

Sorted by: Reset to default 2

You would need to do two things:

1) group your Id to get the count

2) set the count value as height attribute for d3 rect

The below code will group your id by indexing it. The length of the groupId would be the count for mon id inside your data:

var groupId = [];
var maxId = 0;
for (var i = 0; i < data.length; i++){
    var item = data[i];

    if (!groupId[item.id]){
        groupId[item.id] = [];
    }

    groupId[item.id].push({name: item.name, color:item.color});

    if (maxId < item.id){
        maxId = item.id;
    }
}

Then for your d3

//Make an SVG Container
var svgContainer = d3.select("body").append("svg").attr("width", 200).attr("height", 200);

for (var i = 1; i <= maxId; i++){

    console.log("length of groupId is " + groupId[i].length);
    console.log("Id is " + i);
    for (var j = 0; j < groupId[i].length; j++){
         console.log("name is " + groupId[i][j].name + " color is " + groupId[i][j].color);
    }
    console.log("===========================");
 //Draw the Rectangle
 var rectangle = svgContainer
                 .append("rect")
                 .attr("x", i*10)
                 .attr("y", i)
                 .attr("width", 5)
                 .attr("height", groupId[i].length);
}

Check the console log, will help you understand the array better.

Demo JSFiddle

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