I'm making an interactive bar chart in d3, and have come across a problem. The bar chart reads data from a form, but it reads the data as a string. When I am using the data to draw bars like this:

var bars = svg.selectAll(rect)

    .data(dataset)

    .enter()

    .append(rect)

    .attr(x, function(d,i) {

        return i * (w / dataset.length);

    })

    .attr(y, function(d) {

        return h - (d * 4);

    })

    .attr(width, w / dataset.length - barPadding)

    .attr(height, function(d) {

        return d * 4;

    })

    .attr(fill, function(d) {

        return rgb( + (d * redLevel) + , 0,  + (d * blueLevel) + );

    });

the data is read as a string. I could use parseInt(d) every time I wanted to use d, but that would be grossly inefficient. It would be easy to do var d = parseInt(d) outside of the method chain, but that wouldn't work with d3. Suggestions?