Instead of bisectBy, replace bisector.

For backwards-compatibility, bisector checks the arity of the specified
function, and if the function only takes a single argument, it is wrapped with a
suitable comparator.

d3.js

@@ -130,13 +130,13 @@
       }
     };
   }
-  var d3_bisect = (d3.bisectBy = d3_bisector)(d3_ascending);
+  var d3_bisect = d3_bisector(d3_ascending);
   d3.bisectLeft = d3_bisect.left;
   d3.bisect = d3.bisectRight = d3_bisect.right;
   d3.bisector = function(f) {
-    return d3_bisector(function(d, x) {
+    return d3_bisector(f.length === 1 ? function(d, x) {
       return d3_ascending(f(d), x);
-    });
+    } : f);
   };
   d3.shuffle = function(array) {
     var m = array.length, t, i;

src/arrays/bisect.js

@@ -25,12 +25,12 @@ function d3_bisector(compare) {
   };
 }
 
-var d3_bisect = (d3.bisectBy = d3_bisector)(d3_ascending);
+var d3_bisect = d3_bisector(d3_ascending);
 d3.bisectLeft = d3_bisect.left;
 d3.bisect = d3.bisectRight = d3_bisect.right;
 
 d3.bisector = function(f) {
-  return d3_bisector(function(d, x) {
-    return d3_ascending(f(d), x);
-  });
+  return d3_bisector(f.length === 1
+      ? function(d, x) { return d3_ascending(f(d), x); }
+      : f);
 };

test/arrays/bisect-test.js

@@ -132,11 +132,11 @@ suite.addBatch({
     }
   },
 
-  "bisectBy(comparator)": {
-    topic: load("arrays/bisect").expression("d3.bisectBy"),
+  "bisector(comparator)": {
+    topic: load("arrays/bisect").expression("d3.bisector"),
     "left": {
-      topic: function(bisectBy) {
-        return bisectBy(function(d, x) { return _.descending(d.key, x); }).left;
+      topic: function(bisector) {
+        return bisector(function(d, x) { return _.descending(d.key, x); }).left;
       },
       "finds the index of an exact match": function(bisect) {
         var array = [{key: 3}, {key: 2}, {key: 1}];
@@ -195,8 +195,8 @@ suite.addBatch({
       }
     },
     "right": {
-      topic: function(bisectBy) {
-        return bisectBy(function(d, x) { return _.ascending(d.key, x); }).right;
+      topic: function(bisector) {
+        return bisector(function(d, x) { return _.ascending(d.key, x); }).right;
       },
       "finds the index after an exact match": function(bisect) {
         var array = [{key: 1}, {key: 2}, {key: 3}];