var data = [];
var i=0;
for (i=0;i<50000;i++) {
 data.push([Math.random(),Math.random()])
}
var swapedData = [];

console.log(+new Date())  //1332356389339
for (i=0;i<data.length;i++){
  swapedData[i] = [data[i][1], data[i][0],]
}
console.log(+new Date()) //1332356389548