d3js selection.each() callback group argument

d3.js

Solution

It's for nested selectors: http://bost.ocks.org/mike/nest/

e.g. for this HTML:

<table>
    <tr>
        <td></td>
        <td></td>
    </tr>
    <tr>
        <td></td>
        <td></td>
    </tr>
</table>

Let's select td:

var el = d3.selectAll("tr").selectAll("td");

el is `[ Array[2] , Array[2] ]`

and `el.each`:

el.each(function() { 
    console.log('args',arguments);
});

Output:

args [undefined, 0, 0]
args [undefined, 1, 0]
args [undefined, 0, 1]
args [undefined, 1, 1]

Problem

Simple html: ``` <div class="div1"> <div class="test"><span>1</span></div> <div class="test"><span>2</span></div> </div> ``` And js: ``` var el = d3.select(".div1").selectAll(".test"); el.each(function() { console.log(arguments); }); ``` Output: ``` [undefined, 0, 0] [undefined, 1, 0] ``` What is the latest argument (0)? According to source code this is group, but I can't find anything about selector groups in d3 documentation. Thanks.

Original source