added normal generator

lib/datakit.js

@@ -71,7 +71,6 @@ var sd = function(arr){
   }
   // return prod([s_sq,1/arr.length]) - Math.pow(prod([s,1/arr.length]),2);
 }
-
 var csv = function(path,callback){
   fs.readFile(path,function(err,data){
     var reg = new RegExp('\r','g');
@@ -92,6 +91,7 @@ var csv = function(path,callback){
     callback(res);
   });
 }
+
 //Given an array of objects (arr), get all values associated with a key (key).
 var col = function(arr,key){
   var res = [];
@@ -110,7 +110,33 @@ var uni = function(n){
   return res;
 }
 
-//potential additions
-// cor, order stats, rnorm, binom
-// plotting
+var norm = function(n,mu,sig){
+  mu = mu || 0;
+  sig = sig || 1;
+
+  //makes a pair of normals with specified parameters via Box-Muller
+  function box(mu_,sig_){
+    var u1 = Math.random();
+    var u2 = Math.random();
+    var z1 = Math.sqrt(-2*Math.log(u1))*Math.cos(2*u2*Math.PI);
+    var z2 = Math.sqrt(-2*Math.log(u1))*Math.sin(2*u2*Math.PI);
+    return [(mu_+(sig_*z1)),(mu_+(sig_*z2))];
+  }
+  var res = [];
+  if (n % 2 == 0){
+    var iter = n/2;
+  }
+  else{
+    var iter = (n-1)/2;
+    res.push(box(mu,sig).pop());
+  }
+  for (var i=0; i<iter;i++){
+    res = res.concat(box(mu,sig));
+  }
+  return res;
+}
 
+// additions
+// replace col with sql style select
+// cor, order stats
+// plotting