Callback function question

In this case, it doesn't matter whether the callback function returns it or not. In fact, it's kind of silly that the function was in there to begin with. I changed that line to

.attr("transform", "rotate(-65)")

with no problem. Normally, we use the callback function to change the return value based on the data. That would look something like this:

.attr("transform", function(d){
           return "rotate(" + (d * 2) + ")";
})

To understand the difference, remember that d3 is traversing through the data you give it one piece at a time. Rotating "all the elements" usually means that all of the elements get rotated by the same amount, and more to the point, there's only one rotation value for all of the elements. This is what we're doing in the workspaces example by setting it to rotate(-65) - every element gets this same value. We wouldn't want to rotate "each element" because this implies that each element would get rotated differently, and in the case of making an x-axis, that would make the text less readable. We do use this for positioning and sizing the dots, like this:

dots.attr('r', 5)
          .attr('cx', function(d) {
            date = parseTime.parse(d.DATE);
            return xScale(date)
          })
          .attr('cy', function(d) {
            return yScale(d.TMAX)
          })
          .style('stroke', '#00ffd2')
          .style('fill', '#006bff');

The attributes 'r', 'cx', and 'cy' are all calculated based on the data that is fed into the function chain. Even if, by some accident of nature or laziness in data collection, they were calculated to be the same, we are still changing "each element" rather than "all elements".

Hope this helps.