Add arc diagram layout function

arcdiagram/README.md

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+# d3.arcdiagram
+
+A plugin for rendering
+[Arc Diagrams](http://en.wikipedia.org/wiki/Arc_diagram).
+Examples:
+
+* http://bl.ocks.org/goodmami/fd03b250588e1e1143bd
+* http://bl.ocks.org/goodmami/41d4ecc7520b73c21538

arcdiagram/arcdiagram.js

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+(function() {
+  d3.arcDiagram = function() {
+    var sortNodes,
+      sortLinks = arcDiagramSortLinks,
+      linkLevel = arcDiagramLinkLevelCompact,
+      nodeWidth = 0,
+      separation = 1,
+      nodeXOffset = 0,
+      levelHeight = arcDiagramLevelHeight,
+      nodes = [],
+      links = [];
+
+    function arc() {
+      var levelIndex = d3.range(nodes.length).map(function() { return []; }),
+        nw = typeof nodeWidth === "function" ? nodeWidth : function() { return nodeWidth; },
+        sep = typeof separation === "function" ? separation : function() { return separation; },
+        nxo = typeof nodeXOffset === "function" ? nodeXOffset : function() { return nodeXOffset; },
+        lh = typeof levelHeight === "function" ? levelHeight : function() { return levelHeight; },
+        curX = 0,
+        nodeIndexMap, idx1, idx2;
+
+      // node calculations
+      nodes.forEach(function(n, i) { n.index = i; });
+      // if sorting nodes, do it here and create a mapping from old to
+      // new positions
+      nodeIndexMap = {};
+      if (sortNodes) nodes.sort(sortNodes);
+      nodes.forEach(function(n, i) {
+        nodeIndexMap[n.index] = i; n.index = i;
+        // while we're iterating, we can set the x, dx, and y values
+        n.x = curX + nxo(n);
+        curX += nw(n) + sep(n);
+        n.y = 0;
+      });
+
+      // link calculations
+      // first, reassign source and index, if necessary.
+      links.forEach(function(link) {
+        link.source = nodeIndexMap[link.source] || link.source;
+        link.target = nodeIndexMap[link.target] || link.target;
+        // also set distance, which is useful for sorting.
+        link.distance = Math.abs(link.source - link.target);
+      });
+      if (sortLinks) links.sort(sortLinks);
+
+      // now we can find the level of each link
+      links.forEach(function(link) {
+        link.level = linkLevel(link, levelIndex);
+        arcDiagramUpdateLevelIndex(link, levelIndex);
+        // and while we're iterating, set the position values
+        link.x1 = (nodes[link.source] || {}).x;
+        link.x2 = (nodes[link.target] || {}).x;
+        link.height = lh(link);
+      });
+    }
+
+    arc.sortNodes = function(x) {
+      if (!arguments.length) return sortNodes;
+      sortNodes = x;
+      return arc;
+    }
+
+    arc.sortLinks = function(x) {
+      if (!arguments.length) return sortLinks;
+      sortLinks = x;
+      return arc;
+    }
+
+    arc.linkLevel = function(x) {
+      if (!arguments.length) return linkLevel;
+      if (x.toLowerCase() == "compact")
+        linkLevel = arcDiagramLinkLevelCompact;
+      else if (x.toLowerCase() == "distance")
+        linkLevel = arcDiagramLinkLevelDistance;
+      else
+        linkLevel = x;
+      return arc;
+    }
+
+    arc.nodeWidth = function(x) {
+      if (!arguments.length) return nodeWidth;
+      nodeWidth = typeof x === "function" ? x : +x;
+      return arc;
+    }
+
+    arc.separation = function(x) {
+      if (!arguments.length) return separation;
+      separation = typeof x === "function" ? x : +x;
+      return arc;
+    }
+
+    arc.nodeXOffset = function(x) {
+      if (!arguments.length) return nodeXOffset;
+      nodeXOffset = typeof x === "function" ? x : +x;
+      return arc;
+    }
+
+    arc.levelHeight = function(x) {
+      if (!arguments.length) return levelHeight;
+      levelHeight = typeof x === "function" ? x : +x;
+      return arc;
+    }
+
+    arc.nodes = function(x) {
+      if (!arguments.length) return nodes;
+      nodes = x;
+      return arc;
+    }
+
+    arc.links = function(x) {
+      if (!arguments.length) return links;
+      links = x;
+      return arc;
+    }
+
+    return arc;
+  }
+
+  function arcDiagramSortLinks(a, b) { return a.distance - b.distance; }
+
+  function arcDiagramLinkLevelCompact(link, levelIndex) {
+    var level = 1, idx1, idx2;
+
+    if (link.source <= link.target) {
+      idx1 = link.source; idx2 = link.target;
+    } else {
+      idx1 = link.target; idx2 = link.source;
+    }
+
+    for (var i = idx1; i < idx2; i++) {
+      if (levelIndex[i][level]) {
+        level += 1;
+        i = idx1 - 1;  // restart the for-loop
+        continue;
+      }
+    }
+    return level;
+  }
+
+  function arcDiagramLinkLevelDistance(link, levelIndex) {
+    return link.distance;
+  }
+
+  function arcDiagramLevelHeight(link) {
+    return link.level;
+  }
+
+  function arcDiagramUpdateLevelIndex(link, levelIndex) {
+    var idx1, idx2;
+    if (link.source <= link.target) {
+      idx1 = link.source; idx2 = link.target;
+    } else {
+      idx1 = link.target; idx2 = link.source;
+    }
+    d3.range(idx1, idx2).forEach(function(i) { levelIndex[i][link.level] = true; });
+  }
+})();