Sankey Gradients

.block

height: 300
border: no
license: MIT

README.md

here all of the link path gradients render 😀

sankey
  .nodes(graph.nodes)
  .links(graph.links)
  .layout(13); // any value > 13 breaks the link gradient

an iteration on by Patient Flow Sankey Particles from @micahstubbs

see also the broken version with 14 layout iterations

inspired by the blog post Data-based and unique gradients for visualizations with d3.js and associated example Data based gradients - Simple - Solar system from @nadiehbremer

d3.sankey.js

d3.sankey = function() {
  var sankey = {},
      nodeWidth = 24,
      nodePadding = 8,
      size = [1, 1],
      nodes = [],
      links = [];

  sankey.nodeWidth = function(_) {
    if (!arguments.length) return nodeWidth;
    nodeWidth = +_;
    return sankey;
  };

  sankey.nodePadding = function(_) {
    if (!arguments.length) return nodePadding;
    nodePadding = +_;
    return sankey;
  };

  sankey.nodes = function(_) {
    if (!arguments.length) return nodes;
    nodes = _;
    return sankey;
  };

  sankey.links = function(_) {
    if (!arguments.length) return links;
    links = _;
    return sankey;
  };

  sankey.size = function(_) {
    if (!arguments.length) return size;
    size = _;
    return sankey;
  };

  sankey.layout = function(iterations) {
    computeNodeLinks();
    computeNodeValues();
    computeNodeBreadths();
    computeNodeDepths(iterations);
    computeLinkDepths();
    return sankey;
  };

  sankey.relayout = function() {
    computeLinkDepths();
    return sankey;
  };

  sankey.link = function() {
    var curvature = .5;

    function link(d) {
      var x0 = d.source.x + d.source.dx,
          x1 = d.target.x,
          xi = d3.interpolateNumber(x0, x1),
          x2 = xi(curvature),
          x3 = xi(1 - curvature),
          y0 = d.source.y + d.sy + d.dy / 2,
          y1 = d.target.y + d.ty + d.dy / 2;
      return "M" + x0 + "," + y0
           + "C" + x2 + "," + y0
           + " " + x3 + "," + y1
           + " " + x1 + "," + y1;
    }

    link.curvature = function(_) {
      if (!arguments.length) return curvature;
      curvature = +_;
      return link;
    };

    return link;
  };

  // Populate the sourceLinks and targetLinks for each node.
  // Also, if the source and target are not objects, assume they are indices.
  function computeNodeLinks() {
    nodes.forEach(function(node) {
      node.sourceLinks = [];
      node.targetLinks = [];
    });
    links.forEach(function(link) {
      var source = link.source,
          target = link.target;
      if (typeof source === "number") source = link.source = nodes[link.source];
      if (typeof target === "number") target = link.target = nodes[link.target];
      source.sourceLinks.push(link);
      target.targetLinks.push(link);
    });
  }

  // Compute the value (size) of each node by summing the associated links.
  function computeNodeValues() {
    nodes.forEach(function(node) {
      node.value = Math.max(
        d3.sum(node.sourceLinks, value),
        d3.sum(node.targetLinks, value)
      );
    });
  }

  // Iteratively assign the breadth (x-position) for each node.
  // Nodes are assigned the maximum breadth of incoming neighbors plus one;
  // nodes with no incoming links are assigned breadth zero, while
  // nodes with no outgoing links are assigned the maximum breadth.
  function computeNodeBreadths() {
    var remainingNodes = nodes,
        nextNodes,
        x = 0;

    while (remainingNodes.length) {
      nextNodes = [];
      remainingNodes.forEach(function(node) {
        node.x = x;
        node.dx = nodeWidth;
        node.sourceLinks.forEach(function(link) {
          if (nextNodes.indexOf(link.target) < 0) {
            nextNodes.push(link.target);
          }
        });
      });
      remainingNodes = nextNodes;
      ++x;
    }

    //
    moveSinksRight(x);
    scaleNodeBreadths((size[0] - nodeWidth) / (x - 1));
  }

  function moveSourcesRight() {
    nodes.forEach(function(node) {
      if (!node.targetLinks.length) {
        node.x = d3.min(node.sourceLinks, function(d) { return d.target.x; }) - 1;
      }
    });
  }

  function moveSinksRight(x) {
    nodes.forEach(function(node) {
      if (!node.sourceLinks.length) {
        node.x = x - 1;
      }
    });
  }

  function scaleNodeBreadths(kx) {
    nodes.forEach(function(node) {
      node.x *= kx;
    });
  }

  function computeNodeDepths(iterations) {
    var nodesByBreadth = d3.nest()
        .key(function(d) { return d.x; })
        .sortKeys(d3.ascending)
        .entries(nodes)
        .map(function(d) { return d.values; });

    //
    initializeNodeDepth();
    resolveCollisions();
    for (var alpha = 1; iterations > 0; --iterations) {
      relaxRightToLeft(alpha *= .99);
      resolveCollisions();
      relaxLeftToRight(alpha);
      resolveCollisions();
    }

    function initializeNodeDepth() {
      var ky = d3.min(nodesByBreadth, function(nodes) {
        return (size[1] - (nodes.length - 1) * nodePadding) / d3.sum(nodes, value);
      });

      nodesByBreadth.forEach(function(nodes) {
        nodes.forEach(function(node, i) {
          node.y = i;
          node.dy = node.value * ky;
        });
      });

      links.forEach(function(link) {
        link.dy = link.value * ky;
      });
    }

    function relaxLeftToRight(alpha) {
      nodesByBreadth.forEach(function(nodes, breadth) {
        nodes.forEach(function(node) {
          if (node.targetLinks.length) {
            var y = d3.sum(node.targetLinks, weightedSource) / d3.sum(node.targetLinks, value);
            node.y += (y - center(node)) * alpha;
          }
        });
      });

      function weightedSource(link) {
        return center(link.source) * link.value;
      }
    }

    function relaxRightToLeft(alpha) {
      nodesByBreadth.slice().reverse().forEach(function(nodes) {
        nodes.forEach(function(node) {
          if (node.sourceLinks.length) {
            var y = d3.sum(node.sourceLinks, weightedTarget) / d3.sum(node.sourceLinks, value);
            node.y += (y - center(node)) * alpha;
          }
        });
      });

      function weightedTarget(link) {
        return center(link.target) * link.value;
      }
    }

    function resolveCollisions() {
      nodesByBreadth.forEach(function(nodes) {
        var node,
            dy,
            y0 = 0,
            n = nodes.length,
            i;

        // Push any overlapping nodes down.
        nodes.sort(ascendingDepth);
        for (i = 0; i < n; ++i) {
          node = nodes[i];
          dy = y0 - node.y;
          if (dy > 0) node.y += dy;
          y0 = node.y + node.dy + nodePadding;
        }

        // If the bottommost node goes outside the bounds, push it back up.
        dy = y0 - nodePadding - size[1];
        if (dy > 0) {
          y0 = node.y -= dy;

          // Push any overlapping nodes back up.
          for (i = n - 2; i >= 0; --i) {
            node = nodes[i];
            dy = node.y + node.dy + nodePadding - y0;
            if (dy > 0) node.y -= dy;
            y0 = node.y;
          }
        }
      });
    }

    function ascendingDepth(a, b) {
      return a.y - b.y;
    }
  }

  function computeLinkDepths() {
    nodes.forEach(function(node) {
      node.sourceLinks.sort(ascendingTargetDepth);
      node.targetLinks.sort(ascendingSourceDepth);
    });
    nodes.forEach(function(node) {
      var sy = 0, ty = 0;
      node.sourceLinks.forEach(function(link) {
        link.sy = sy;
        sy += link.dy;
      });
      node.targetLinks.forEach(function(link) {
        link.ty = ty;
        ty += link.dy;
      });
    });

    function ascendingSourceDepth(a, b) {
      return a.source.y - b.source.y;
    }

    function ascendingTargetDepth(a, b) {
      return a.target.y - b.target.y;
    }
  }

  function center(node) {
    return node.y + node.dy / 2;
  }

  function value(link) {
    return link.value;
  }

  return sankey;
};

data.json

{
  "nodes": [
    {
      "name": "All referred patients",
      "id": 0
    },
    {
      "name": "First consult outpatient clinic",
      "id": 1
    },
    {
      "name": "No OR-receipt",
      "id": 2
    },
    {
      "name": "OR-receipt",
      "id": 3
    },
    {
      "name": "No surgery",
      "id": 4
    },
    {
      "name": "Start surgery",
      "id": 5
    },
    {
      "name": "Emergency",
      "id": 6
    },
    {
      "name": "No emergency",
      "id": 7
    }
  ],
  "links": [
    {
      "source": 0,
      "target": 1,
      "value": 1,
      "label": 1
    },
    {
      "source": 1,
      "target": 2,
      "value": 0.64,
      "label": 0.64
    },    
    {
      "source": 1,
      "target": 3,
      "value": 0.36,
      "label": 0.36
    },
    {
      "source": 3,
      "target": 4,
      "value": 0.1188,
      "label": 0.33
    },
    {
      "source": 3,
      "target": 5,
      "value": 0.2412,
      "label": 0.67
    },
    {
      "source": 5,
      "target": 6,
      "value": 0.038592,
      "label": 0.16
    },
    {
      "source": 5,
      "target": 7,
      "value": 0.20260799999999998,
      "label": 0.84
    }
  ]
}

index.html

<!DOCTYPE html>
<meta charset='utf-8'>
<title>Sankey Gradients</title>
<script src='https://cdnjs.cloudflare.com/ajax/libs/d3/4.4.0/d3.min.js'></script>
<script src='d3.sankey.js'></script>
<script src='https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.19.0/babel.min.js'></script>
<style>
.node rect {
  cursor: move;
  fill-opacity: .9;
  shape-rendering: crispEdges;
}
 
.node text {
  pointer-events: none;
  font-family: Helvetica;
  font-size: 12px;
}
</style>
<body>
<div id='chart'>
<script lang='babel' type='text/babel'>
const units = '';
const margin = {top: 10, right: 10, bottom: 10, left: 10};
const width = 960 - margin.left - margin.right;
const height = 300 - margin.top - margin.bottom;

// zero decimal places
const formatNumber = d3.format(',.0f');

const format = d => `${formatNumber(d)} ${units}`;

const color = d3.scaleOrdinal()
  .domain([
    'All referred patients',
    'First consult outpatient clinic',
    'OR-receipt',
    'Start surgery',
    // 'No OR-receipt',
    // 'No emergency',
    // 'No surgery',
    'Emergency'
  ])
  .range([
    '#90eb9d',
    '#f9d057',
    '#f29e2e',
    '#00ccbc',
    '#d7191c'
  ]);

d3.select('#chart')
  .style('visibility', 'visible');

// append the svg canvas to the page
const svg = d3.select('#chart').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})`);

// set the sankey diagram properties
const sankey = d3.sankey()
  .nodeWidth(12)
  .nodePadding(10)
  .size([width, height]);

const path = sankey.link();

// append a defs (for definition) element to your SVG
const defs = svg.append('defs');

// load the data
d3.json('data.json', (error, graph) => {
  console.log('graph', graph);
  sankey
    .nodes(graph.nodes)
    .links(graph.links)
    .layout(13); // any value > 13 breaks the link gradient
 
  // add in the links
  const link = svg.append('g').selectAll('.link')
    .data(graph.links)
    .enter().append('path')
      .attr('class', 'link')
      .attr('d', path)
      .style('stroke-width', d => Math.max(1, d.dy))
      .style('fill', 'none')
      .style('stroke-opacity', 0.18)
      .sort((a, b) => b.dy - a.dy)
      .on('mouseover', function() {
        d3.select(this).style('stroke-opacity', 0.5);
      })
      .on('mouseout', function() {
        d3.select(this).style('stroke-opacity', 0.2);
      });
 
  // add the link titles
  link.append('title')
    .text(d => `${d.source.name} → ${d.target.name}\n${format(d.value)}`);
 
  // add in the nodes
  const node = svg.append('g').selectAll('.node')
    .data(graph.nodes)
    .enter().append('g')
      .attr('class', 'node')
      .attr('transform', d => `translate(${d.x},${d.y})`)
      .call(d3.drag()
        .subject(d => d)
        .on('start', function() { 
          this.parentNode.appendChild(this); })
        .on('drag', dragmove));
 
  // add the rectangles for the nodes
  node.append('rect')
    .attr('height', d => d.dy)
    .attr('width', sankey.nodeWidth())
    .style('fill', d => { 
      if(color.domain().indexOf(d.name) > -1){
        return d.color = color(d.name);  
      } else {
        return d.color = '#ccc';
      }
    })
    .append('title')
      .text(d => `${d.name}\n${format(d.value)}`);
 
  // add in the title for the nodes
  node.append('text')
    .attr('x', -6)
    .attr('y', d => d.dy / 2)
    .attr('dy', '.35em')
    .attr('text-anchor', 'end')
    .attr('transform', null)
    .text(d => d.name)
    .filter(d => d.x < width / 2)
      .attr('x', 6 + sankey.nodeWidth())
      .attr('text-anchor', 'start');

  // add gradient to links
  link.style('stroke', (d, i) => {
    console.log('d from gradient stroke func', d);

    // make unique gradient ids  
    const gradientID = `gradient${i}`;

    const startColor = d.source.color;
    const stopColor = d.target.color;

    console.log('startColor', startColor);
    console.log('stopColor', stopColor);

    const linearGradient = defs.append('linearGradient')
        .attr('id', gradientID);

    linearGradient.selectAll('stop') 
      .data([                             
          {offset: '10%', color: startColor },      
          {offset: '90%', color: stopColor }    
        ])                  
      .enter().append('stop')
      .attr('offset', d => {
        console.log('d.offset', d.offset);
        return d.offset; 
      })   
      .attr('stop-color', d => {
        console.log('d.color', d.color);
        return d.color;
      });

    return `url(#${gradientID})`;
  })
 
// the function for moving the nodes
  function dragmove(d) {
    d3.select(this).attr('transform', 
      `translate(${d.x = Math.max(0, Math.min(width - d.dx, d3.event.x))},${d.y = Math.max(0, Math.min(height - d.dy, d3.event.y))})`);
    sankey.relayout();
    link.attr('d', path);
  }
});
</script>
</body>
</html>

preview.png

preview.xcf

thumbnail.png

Thanks for the idea - I took your script and adjusted it to the latest version of d3 (0.6). Unfortunately, I have one link that will not be rendered correctly. I removed the opacity for development reasons.

Live example:
https://bl.ocks.org/wiesson/87c7714081e1b1f24e5b36b4335b09c2

Any ideas?