d3 multiple graph not working

I am having problem when generating 15 line-chars from 15 .csv files by using a for loop. Instead of locating each graph in a different div, 15 graphs all overlapped in the last div.

Thank you in advance.

for (var i = 0; i<15; i++) { 

        var svg = d3.select("#graph_"+i)
        .append("svg")
                .attr("width", width + margin.left + margin.right)
                .attr("height", height + margin.top + margin.bottom)
        .append("g")
                .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

// Get the data
d3.csv(folder.toString()+"/"+i+".csv", function(error, data) {
        data.forEach(function(d) {
                d.x = +d.x;
                d.y = +d.y;
        });

        // Scale the range of the data
        x.domain(d3.extent(data, function(d) { return d.x; }));
        y.domain([0, d3.max(data, function(d) { return d.y; })]);

        // Add the valueline path.
        svg.append("path")
                .attr("class", "line")
                .attr("d", valueline(data));

        // Add the X Axis
        svg.append("g")
                .attr("class", "x axis")
                .attr("transform", "translate(0," + height + ")")
                .call(xAxis);

        // Add the Y Axis
        svg.append("g")
                .attr("class", "y axis")
                .call(yAxis);

});

        }