08-27-周三_17-09-29

node_modules/dagre-layout/lib/order/cross-count.js

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+import _ from 'lodash'
+
+/*
+ * A function that takes a layering (an array of layers, each with an array of
+ * ordererd nodes) and a graph and returns a weighted crossing count.
+ *
+ * Pre-conditions:
+ *
+ *    1. Input graph must be simple (not a multigraph), directed, and include
+ *       only simple edges.
+ *    2. Edges in the input graph must have assigned weights.
+ *
+ * Post-conditions:
+ *
+ *    1. The graph and layering matrix are left unchanged.
+ *
+ * This algorithm is derived from Barth, et al., "Bilayer Cross Counting."
+ */
+function crossCount (g, layering) {
+  let cc = 0
+  for (let i = 1; i < layering.length; ++i) {
+    cc += twoLayerCrossCount(g, layering[i - 1], layering[i])
+  }
+  return cc
+}
+
+function twoLayerCrossCount (g, northLayer, southLayer) {
+  // Sort all of the edges between the north and south layers by their position
+  // in the north layer and then the south. Map these edges to the position of
+  // their head in the south layer.
+  const southPos = _.zipObject(southLayer,
+    _.map(southLayer, function (v, i) { return i }))
+  const southEntries = _.flatten(_.map(northLayer, function (v) {
+    return _.chain(g.outEdges(v))
+      .map(function (e) {
+        return { pos: southPos[e.w], weight: g.edge(e).weight }
+      })
+      .sortBy('pos')
+      .value()
+  }), true)
+
+  // Build the accumulator tree
+  let firstIndex = 1
+  while (firstIndex < southLayer.length) {
+    firstIndex <<= 1
+  }
+  const treeSize = 2 * firstIndex - 1
+  firstIndex -= 1
+  const tree = _.map(new Array(treeSize), function () { return 0 })
+
+  // Calculate the weighted crossings
+  let cc = 0
+  _.forEach(southEntries.forEach(function (entry) {
+    let index = entry.pos + firstIndex
+    tree[index] += entry.weight
+    let weightSum = 0
+    while (index > 0) {
+      if (index % 2) {
+        weightSum += tree[index + 1]
+      }
+      index = (index - 1) >> 1
+      tree[index] += entry.weight
+    }
+    cc += entry.weight * weightSum
+  }))
+
+  return cc
+}
+
+export default crossCount