divide by two (grids)

<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
  font-family: Helvetica;
  font-size: 10px;
}

rect {
  fill: none;
  stroke: black;
  stroke-width: 1;
}
</style>
<body>
<script src="https://d3js.org/d3.v4.js"></script>
<script src="https://romsson.github.io/d3-gridding/build/d3-gridding.js"></script>
<script>

var width = 600,
    height = 400;

var gridding = d3.gridding()
  .size([width, height])
  .mode("horizontal");

var data = d3.range(20);

var griddingData = gridding(data);

var svgSquares = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g");

svgSquares.selectAll(".square")
    .data(griddingData, function(d) { return d.index; })
  .enter().append("rect")
    .attr("class", "square")
    .attr("width", function(d) { return d.width; })
    .attr("height", function(d) { return d.height; })
    .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; })

griddingData.map(function(d, i) {

var grid = d3.gridding()
    .size([d.width, d.height])
    .offset([d.x, d.y])
    .mode("vertical");

griddingDataSub = grid(d3.range(i + 1));

svgSquares.selectAll(".square_" + i)
      .data(griddingDataSub, function(d) { return d.index; })
    .enter().append("rect")
      .attr("class", "square_" + i)
      .attr("width", function(d) { return d.width; })
      .attr("height", function(d) { return d.height; })
      .attr("transform", function(d) {
        return "translate(" + d.x + "," + d.y + ")";
      });

//svgSquares.selectAll(".index_" + i)
  //    .data(griddingDataSub)
  //  .enter().append("text")
  //    .attr("class", ".index_" + i)
  //    .style('text-anchor', 'middle')
  //    .style('dominant-baseline', 'central')
  //    .style("font-size", function(d) { return d.height / 2; })
  //    .attr("transform", function(d) {
  //      return "translate(" + d.cx + "," + d.cy + ")";
  //    })
  //    .text(function(d, i) { return d.__value; });

});

</script>
</body>

Modified http://d3js.org/d3.v4.js to a secure url

Modified http://romsson.github.io/d3-gridding/build/d3-gridding.js to a secure url

https://d3js.org/d3.v4.js

https://romsson.github.io/d3-gridding/build/d3-gridding.js