Add d3.sum and d3.stats.median.

Makefile

@@ -39,6 +39,7 @@ d3.core.js: \
 	src/core/descending.js \
 	src/core/min.js \
 	src/core/max.js \
+	src/core/sum.js \
 	src/core/nest.js \
 	src/core/keys.js \
 	src/core/values.js \
@@ -101,6 +102,7 @@ d3.stats.js: \
 	src/stats/kde.js \
 	src/stats/iqr.js \
 	src/stats/mean.js \
+	src/stats/median.js \
 	src/stats/quantiles.js \
 	src/stats/variance.js \
 	src/end.js
@@ -179,6 +181,7 @@ tests: \
 	tests/test-scale-log.test \
 	tests/test-scale-sqrt.test \
 	tests/test-scale-pow.test \
+	tests/test-stats-median.test \
 	tests/test-svg-arc.test \
 	tests/test-svg-area.test \
 	tests/test-svg-line.test \

d3.js

@@ -66,6 +66,13 @@ d3.max = function(array, f) {
   }
   return a;
 };
+d3.sum = function(x) {
+  var s = 0,
+      n = x.length,
+      i = -1;
+  while (++i < n) s += x[i];
+  return s;
+};
 d3.nest = function() {
   var nest = {},
       keys = [],

d3.stats.js

@@ -100,12 +100,13 @@ d3.stats.iqr = function(x) {
   return quartiles[1] - quartiles[0];
 };
 d3.stats.mean = function(x) {
-  var s = 0,
-      n = x.length,
-      i = -1;
-  while (++i < n) s += x[i];
-  return s / n;
+  return d3.sum(x) / x.length;
 }
+d3.stats.median = function(x) {
+  var i = x.length / 2,
+      j = Math.floor(i);
+  return i === j ? (x[j - 1] + x[j]) / 2 : x[j];
+};
 d3.stats.quantiles = function(d, quantiles) {
   d = d.slice().sort(d3.ascending);
   var n = d.length;

d3.stats.min.js

@@ -1 +1 @@
-(function(){d3.stats={},d3.stats.bandwidth={nrd0:function(a){var b=Math.sqrt(d3.stats.variance(a));(lo=Math.min(b,d3.stats.iqr(a)/1.34))||(lo=b)||(lo=Math.abs(a[1]))||(lo=1);return.9*lo*Math.pow(a.length,-0.2)},nrd:function(a){var b=d3.stats.quantiles(a,[.25,.75]),c=(b[1]-b[0])/1.34;return 1.06*Math.min(Math.sqrt(d3.stats.variance(a)),c)*Math.pow(a.length,-0.2)}},d3.stats.kernel={uniform:function(a){if(a<=1&&a>=-1)return.5;return 0},triangular:function(a){if(a<=1&&a>=-1)return 1-Math.abs(a);return 0},epanechnikov:function(a){if(a<=1&&a>=-1)return.75*(1-a*a);return 0},quartic:function(a){if(a<=1&&a>=-1){var b=1-a*a;return.9375*b*b}return 0},triweight:function(a){if(a<=1&&a>=-1){var b=1-a*a;return 35/32*b*b*b}return 0},gaussian:function(a){return 1/Math.sqrt(2*Math.PI)*Math.exp(-0.5*a*a)},cosine:function(a){if(a<=1&&a>=-1)return Math.PI/4*Math.cos(Math.PI/2*a);return 0}},d3.stats.kde=function(){function d(d,e){var f=c.call(this,b);return d.map(function(c){var d=-1,e=0,g=b.length;while(++d<g)e+=a((c-b[d])/f);return[c,e/f/g]})}var a=d3.stats.kernel.gaussian,b=[],c=d3.stats.bandwidth.nrd;d.kernel=function(b){if(!arguments.length)return a;a=b;return d},d.sample=function(a){if(!arguments.length)return b;b=a;return d},d.bandwidth=function(a){if(!arguments.length)return c;c=d3.functor(a);return d};return d},d3.stats.iqr=function(a){var b=d3.stats.quantiles(a,[.25,.75]);return b[1]-b[0]},d3.stats.mean=function(a){var b=0,c=a.length,d=-1;while(++d<c)b+=a[d];return b/c},d3.stats.quantiles=function(a,b){a=a.slice().sort(d3.ascending);var c=a.length;return b.map(function(b){b*=c;return~~b===b?(a[b]+a[b+1])/2:a[Math.round(b)]})},d3.stats.variance=function(a){var b=d3.stats.mean(a),c=a.length,d=-1,e=0;while(++d<c){var f=a[d]-b;e+=f*f}return e/(c-1)}})()
+(function(){d3.stats={},d3.stats.bandwidth={nrd0:function(a){var b=Math.sqrt(d3.stats.variance(a));(lo=Math.min(b,d3.stats.iqr(a)/1.34))||(lo=b)||(lo=Math.abs(a[1]))||(lo=1);return.9*lo*Math.pow(a.length,-0.2)},nrd:function(a){var b=d3.stats.quantiles(a,[.25,.75]),c=(b[1]-b[0])/1.34;return 1.06*Math.min(Math.sqrt(d3.stats.variance(a)),c)*Math.pow(a.length,-0.2)}},d3.stats.kernel={uniform:function(a){if(a<=1&&a>=-1)return.5;return 0},triangular:function(a){if(a<=1&&a>=-1)return 1-Math.abs(a);return 0},epanechnikov:function(a){if(a<=1&&a>=-1)return.75*(1-a*a);return 0},quartic:function(a){if(a<=1&&a>=-1){var b=1-a*a;return.9375*b*b}return 0},triweight:function(a){if(a<=1&&a>=-1){var b=1-a*a;return 35/32*b*b*b}return 0},gaussian:function(a){return 1/Math.sqrt(2*Math.PI)*Math.exp(-0.5*a*a)},cosine:function(a){if(a<=1&&a>=-1)return Math.PI/4*Math.cos(Math.PI/2*a);return 0}},d3.stats.kde=function(){function d(d,e){var f=c.call(this,b);return d.map(function(c){var d=-1,e=0,g=b.length;while(++d<g)e+=a((c-b[d])/f);return[c,e/f/g]})}var a=d3.stats.kernel.gaussian,b=[],c=d3.stats.bandwidth.nrd;d.kernel=function(b){if(!arguments.length)return a;a=b;return d},d.sample=function(a){if(!arguments.length)return b;b=a;return d},d.bandwidth=function(a){if(!arguments.length)return c;c=d3.functor(a);return d};return d},d3.stats.iqr=function(a){var b=d3.stats.quantiles(a,[.25,.75]);return b[1]-b[0]},d3.stats.mean=function(a){return d3.sum(a)/a.length},d3.stats.median=function(a){var b=a.length/2,c=Math.floor(b);return b===c?(a[c-1]+a[c])/2:a[c]},d3.stats.quantiles=function(a,b){a=a.slice().sort(d3.ascending);var c=a.length;return b.map(function(b){b*=c;return~~b===b?(a[b]+a[b+1])/2:a[Math.round(b)]})},d3.stats.variance=function(a){var b=d3.stats.mean(a),c=a.length,d=-1,e=0;while(++d<c){var f=a[d]-b;e+=f*f}return e/(c-1)}})()

src/stats/mean.js

@@ -1,7 +1,3 @@
 d3.stats.mean = function(x) {
-  var s = 0,
-      n = x.length,
-      i = -1;
-  while (++i < n) s += x[i];
-  return s / n;
+  return d3.sum(x) / x.length;
 }

tests/test-stats-median.js

@@ -0,0 +1,12 @@
+require("./../lib/env-js/envjs/node");
+require("./../d3");
+require("./../d3.stats");
+
+var data = [1, 2, 3, 4, 5];
+
+for (var i = 0; i <= data.length; i++) {
+  var tmp = data.slice(0, i);
+  console.log("median [" + tmp.join(",") + "]:");
+  console.log("  ", d3.stats.median(tmp));
+  console.log("");
+}

tests/test-stats-median.out

@@ -0,0 +1,18 @@
+median []:
+   NaN
+
+median [1]:
+   1
+
+median [1,2]:
+   1.5
+
+median [1,2,3]:
+   2
+
+median [1,2,3,4]:
+   2.5
+
+median [1,2,3,4,5]:
+   3
+