General Update Pattern, III

By adding transitions, we can more easily follow the elements as they are entered, updated and exited. Separate transitions are defined for each of the three states. To avoid repeating transition timing parameters for the enter, update, and exit selections, a top-level transition t sets the duration, and then subsequent transitions use selection.transition, passing in t to inherit timing:

var t = d3.transition()
    .duration(750);

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See the D3 wiki for even more resources.

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<!DOCTYPE html>
<meta charset="utf-8">
<style>

text {
  font: bold 48px monospace;
}

.enter {
  fill: green;
}

.update {
  fill: #333;
}

.exit {
  fill: brown;
}

</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var alphabet = "abcdefghijklmnopqrstuvwxyz".split("");

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height"),
    g = svg.append("g").attr("transform", "translate(32," + (height / 2) + ")");

function update(data) {
  var t = d3.transition()
      .duration(750);

// JOIN new data with old elements.
  var text = g.selectAll("text")
    .data(data, function(d) { return d; });

// EXIT old elements not present in new data.
  text.exit()
      .attr("class", "exit")
    .transition(t)
      .attr("y", 60)
      .style("fill-opacity", 1e-6)
      .remove();

// UPDATE old elements present in new data.
  text.attr("class", "update")
      .attr("y", 0)
      .style("fill-opacity", 1)
    .transition(t)
      .attr("x", function(d, i) { return i * 32; });

// ENTER new elements present in new data.
  text.enter().append("text")
      .attr("class", "enter")
      .attr("dy", ".35em")
      .attr("y", -60)
      .attr("x", function(d, i) { return i * 32; })
      .style("fill-opacity", 1e-6)
      .text(function(d) { return d; })
    .transition(t)
      .attr("y", 0)
      .style("fill-opacity", 1);
}

// The initial display.
update(alphabet);

// Grab a random sample of letters from the alphabet, in alphabetical order.
d3.interval(function() {
  update(d3.shuffle(alphabet)
      .slice(0, Math.floor(Math.random() * 26))
      .sort());
}, 1500);

</script>

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