问crossfilter中的对数图表

EN

Math.log(d.count) / Math.LN10;

var crossfiltered_data = crossfilter(data),
    all = crossfiltered_data.groupAll(),
    item_labels = crossfiltered_data.dimension(function(d) { return d.name; }),
    items_group = hour.group().reduceSum(function(d) {
        return d.count
    }),
    charts = [
        barChart(on_range_change)
            .dimension(item_labels)
            .group(items_group)
          .x(d3.scale.linear()
            .domain([domain_start, domain_end])
            .rangeRound([0, 240])),
    ],
    chart = d3.selectAll(target)
        .data(charts)
        .each(function(chart) { 
            chart   .on("brush", renderAll)
                    .on("brushend", renderAll);
        }),
    render = function(method) {
            d3.select(this).call(method);
    },
    renderAll = function(event) {
        chart.each(render);
    };