d3-transform makes it easy to define and reuse functions that produce transform attribute strings for SVG elements. Using d3-transform reduces repetition, allows you to compose multiple transforms, and eliminates ugly string-interpolation from your d3 visualization code.

Include d3-transform in your web page using a script tag any time after you've included d3:

<script src="http://d3js.org/d3.v4.min.js"></script>
<script src="d3-transform.js"></script>

d3-transform replaces the manual construction of transform attribute strings for SVG elements. For example, if you want to translate, rotate, and scale a group element depending on the data bound to that element, you'd write something like this without d3-transform:

d3.select('svg').selectAll('g')
 .data([{ size: 5 }, { size: 10 }])
 .enter().append('g')
 .attr('transform', function(d, i) {
 return "translate(20," + d.size * 10 + ") rotate (40) scale(" + ( d.size + 2 ) + ")");
 });

With d3-transform, you can rewrite the above code like this:

var transform = d3.transform()
 .translate(function(d) { return [20, d.size * 10] })
 .rotate(40)
 .scale(function(d) { return d.size + 2 });
var svg = d3.select('svg').selectAll('g')
 .data([{ size: 5 }, { size: 10 }])
 .enter()
 .append('g')
 .attr('transform', transform);

In both cases the resulting document will look the same:

<svg>
 <g transform="translate(20,50) rotate(40) scale(7)"></g>
 <g transform="translate(20,100) rotate(40) scale(12)"></g>
</svg>

You can specify arguments for these operations by either providing positional arguments to the corresponding method of the transform object, or by providing a function that will return an array of arguments that are interpreted as positional arguments. In the special case where an operation only takes one argument, your function can return a number.

All of the SVG 1.1 transform operations are supported: matrix, rotate, translate, scale, skewX, and skewY. See the SVG 1.1 Specification or MDN for further details on the arguments of each operation.

When using node.js, calls to require('d3-transform') return a direct reference to the "transform" method.

var d3 = require('d3');
var d3Transform = require('d3-transform');
var transform = d3Transform()
 .translate(function(d) { return [20, d.size * 10] })
 .rotate(40)
 .scale(function(d) { return d.size + 2 });
var svg = d3.select('svg.example1').selectAll('g')
 .data([{ size: 5 }, { size: 10 }])
 .enter()
 .append('g')
 .attr('transform', transform);

If you want to extend one transform with another set of operations, pass the initial transform object into the d3.transform() function:

var transform1 = d3.transform()
 .translate(10,20);
var transform2 = d3.transform(transform1)
 .scale(function(d) { return [d.size];})
d3.select('svg.example2').selectAll('g')
 .data([{ size: 5 }, { size: 10 }])
 .enter().append('g')
 .attr('transform', transform2);

Another way to compose multiple transform objects is to use the seq operation:

var transform1 = d3.transform()
 .translate(10,20);
var transform2 = d3.transform()
 .scale(function(d) { return [d.size];})
var transform =
 transform1.seq(transform2);

With either of these approaches, the result is a document that looks like this:

<svg>
 <g transform="translate(10,20) scale(5)"></g>
 <g transform="translate(10,20) scale(10)"></g>
</svg>

• Erik Cunningham @trinary
• Spiros Eliopoulos @seliopou
• Micah Stubbs @micahstubbs