Highlight Selection

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<style>
circle {
    fill: #ddd;
}

rect {
    fill: none;
    stroke: #FF9797;
    stroke-width: 1.0;
}

p {
    font-size: 12px;
    margin: 0px;
    padding: 0px;
}
</style>
<script src="https://d3js.org/d3.v3.min.js" charset="utf-8"></script>
<script>

var NUM_ELEMENTS = 16,
    data = [],
    circleSpacing = 30,
    leftMargin = 20;

for (var i = 0; i < NUM_ELEMENTS; i++) {
    data.push(i);
}

var svg = d3.select('body').append('svg')
    .attr('width', 960)
    .attr('height', 50);

var label = d3.select('body').append('p');

svg.selectAll('circle')
    .data(data)
    .enter().append('circle')
    .attr('cx', function(d, i) {
        return (d * circleSpacing) + leftMargin;
    })
    .attr('cy', 20)
    .attr('r', 2);

function updateSelection(selection) {
    // draw rect around each selected circle
    var rectWidth = 20;
    var rectHeight = 30;

var rects = svg.selectAll('rect')
        .data(selection);

// start off screen for nice transition
    rects.enter().append('rect')
        .attr('x', -20)
        .attr('y', 20 - (rectHeight / 2.0))
        .attr('height', rectHeight)
        .attr('width', rectWidth);

rects.transition().duration(600).attr('x', function(d, i) {
            return (d * circleSpacing) + leftMargin - (rectWidth / 2.0);
        })
        .attr('y', 20 - (rectHeight / 2.0))
        .attr('height', rectHeight)
        .attr('width', rectWidth);

rects.exit().transition()
        .attr('x', -20)
        .remove();

label.text('Selection: ' + selection.join(', '));
}

function randomSelect() {
    var numSelected = Math.round(Math.random() * 4),
        selection = shuffle(data.slice(0)).slice(0, numSelected);
    updateSelection(selection);
}

// Shuffles the input array.
function shuffle(array) {
  var m = array.length, t, i;
  while (m) {
    i = Math.floor(Math.random() * m--);
    t = array[m], array[m] = array[i], array[i] = t;
  }
  return array;
}

setInterval(randomSelect, 1000);

</script>

</body>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js