Transition Between Curve Types

.block

license: mit
height: 600
scrolling: no
border: yes

.eslintrc.json

{
    "env": {
        "browser": true
    },
    "extends": "eslint:recommended",
    "globals": {
        "d3": false,
        "ss": false,
        "topojson": false
    },
    "parserOptions": {
        "ecmaFeatures": {
            "impliedStrict": true
        }
    },
    "rules": {
        "indent": ["warn", 4],
        "no-tabs": "error"
    }
}

README.md

This block illustrates how to transition between curve types. We use transition.attrTween to specify a custom interpolator -- called pathTween -- which was borrowed from Mike Bostock's Path Tween block.

For more information, see this discussion on Stack Overflow and the MDN page on the SVG d attribute.

block.js

/* Remember: Use four-space indents.
 * However, use two-space indents for operations that change the selection.
 * For more information, see:
 * https://bost.ocks.org/mike/d3/workshop/#35
 */
var svg = d3.select("svg"),
    margin = {top: 20, right: 90, bottom: 40, left: 40},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom;

var curves = [
    "curveBasis", "curveCardinal", "curveCatmullRom", "curveLinear",
    "curveStepAfter",
]

var g = svg.append("g")
    .attr("transform", translate(margin.left, margin.top));

d3.csv("index_data.csv", row, function (error, index_data) {
    if (error) throw error;

    d3.select("select")
        .on("change", update)
      .selectAll("option")
        .data(curves)
      .enter().append("option")
        .text(function (d) { return d; });

    var x = d3.scaleTime()
        .domain(d3.extent(index_data, function (d) { return d.date; }))
        .range([0, width]);

    var y = d3.scaleLinear()
        .domain([0, 10])
        .range([height, 0]);

    var colour = d3.scaleOrdinal(d3.schemeCategory10);

    var nest = d3.nest()
        .key(function (d) { return d.country; })
        .sortValues(function (a, b) { return d3.ascending(a.date, b.date); })
        .entries(index_data);

    var line = d3.line()
        .x(function (d) { return x(d.date); })
        .y(function (d) { return y(d.score); });

    g.append("g")
        .attr("class", "paths");

    g.append("g")
        .attr("class", "annotations");

    g.append("g")
        .attr("class", "x axis")
        .attr("transform", translate(0, height))
        .call(d3.axisBottom(x).tickFormat(d3.timeFormat("%b")));

    g.append("g")
        .attr("class", "y axis")
        .call(d3.axisLeft(y));

    update();

    function update() {
        line.curve(d3[this.value ? this.value : "curveBasis"]);

        var path = d3.select(".paths").selectAll(".path")
            .data(nest, function (d) { return d.key; });

        path.enter().append("path")
            .attr("class", "path")
            .attr("d", function (d) { return line(d.values); })
            .attr("fill", "none")
            .attr("stroke", function (d) { return colour(d.key); })
            .attr("stroke-width", 2)
          .merge(path)
            .each(transition);

        var annotation = d3.select(".annotations").selectAll(".annotation")
            .data(nest, function (d) { return d.key; });

        annotation.enter().append("text")
            .attr("class", "annotation")
            .attr("x", function (d) { return x(d.values[d.values.length - 1].date); })
            .attr("y", function (d) { return y(d.values[d.values.length - 1].score); })
            .attr("dx", 3)
            .attr("dy", 3)
            .attr("font-family", "Helvetica")
            .attr("font-size", 12)
            .attr("fill", function (d) { return colour(d.key); })
            .text(function (d) { return d.key; });

        function transition(d) {
            d3.select(this).transition()
                .duration(1000)
                .attrTween("d", pathTween(line(d.values), 4));
        }
    }
});

function pathTween(d1, precision) {
    // An interpolator factory: a function that returns a function.
    // d1: The target path (a string containing a series of path descriptions).
    // precision: The precision to sample the source and target paths.
    return function () {
        var path0 = this,
            path1 = path0.cloneNode(),
            n0 = path0.getTotalLength(),
            n1 = (path1.setAttribute("d", d1), path1).getTotalLength();

        // Uniformly sample either the source or target path, whichever is longer.
        var distances = [0],
            i = 0,
            dt = precision / Math.max(n0, n1);

        while ((i += dt) < 1) {
            distances.push(i);
        }

        distances.push(1);

        // Get an interpolator for each pair of points.
        var points = distances.map(function (distance) {
            var p0 = path0.getPointAtLength(distance * n0),
                p1 = path1.getPointAtLength(distance * n1);
            return d3.interpolate([p0.x, p0.y], [p1.x, p1.y]);
        });

        // Here, `p` is the current interpolator.
        // We join the interpolated points using the `Lineto` path command.
        return function(t) {
            return t < 1 ? "M" + points.map(function (p) { return p(t); }).join("L") : d1;
        }
    }
}

function row(d) {
    var tokens = d.date.split("-"),
        year = +tokens[0],
        quarter = +tokens[1].replace("Q", ""),
        month = ((quarter - 1) * 3) + 1;
    d.date = new Date(year, month);
    d.score = +d.score;
    return d;
}

function translate(x, y) {
    return "translate(" + x + "," + y + ")";
}

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<svg width="960" height="500"></svg>
<select></select>
<script src="https://unpkg.com/d3@4/build/d3.min.js"></script>
<script src="block.js"></script>

index_data.csv

LICENSE

MIT License

Copyright (c) 2017 Iain Dillingham

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

preview.png

thumbnail.png