var linear = d3.scale.linear().domain([0,20]).range([0,100]);
console.log( linear(10) );              //输出50
console.log( linear(30) );              //输出150
console.log( linear.invert(80) );              //输出16

linear.clamp(true);
console.log( linear(30) );              //输出100

linear.rangeRound([0,100]);
console.log( linear(13.33) );              //输出67，对结果进行了四舍五入//使用nice之后，定义域变成了比较工整的形式，但是并不是四舍五入
linear.domain([0.12300000,0.4888888888]).nice();
console.log( linear.domain() );              //输出[0.1,0.5]
linear.domain([33.611111,45.97745]).nice();
console.log( linear.domain() );              //输出[33,46]
var linear = d3.scale.linear().domain([-20,20]).range([0,100]);
var ticks = linear.ticks(5);
console.log(ticks);            //输出数组[-20,-10,0,10,20]var tickFormat = linear.tickFormat(5,"+");//设定的格式为"+":表示如果是正数，则在前面添加一个加号，负数则添加一个减号。
for(var i=0;i<ticks.length;i++){ticks[i] = tickFormat(ticks[i]);
}
console.log(ticks);            //输出["-20","-10","+0","+10","+20"]

var pow = d3.scale.pow().exponent(3);     //设置指数比例尺的指数为3
console.log( pow(2) );        //输出为8
console.log( pow(3) );        //输出为27

pow.exponent(0.5);
console.log( pow(2) );        //输出为1.414
console.log( pow(3) );        //输出为1.732
//指定domain和range
//指数比例尺
var pow = d3.scale.pow().exponent(3).domain([0,3])          //指数比例尺内部调用了线性比例尺，而且把这个线性比例尺.range([0,90]);         //定义域的边界变为了其指定的次方。即定义域为[0,27]
//线性比例尺
var linear = d3.scale.linear().domain([0,Math.pow(3,3)]).range([0,90]);
console.log( pow(1.5) );        //输出为11.25
console.log( linear(Math.pow(1.5,3)) );    //输出为11.25

//该阈值比例尺定义了三个阈值：10、20、30，则空间被划分为四段：负无穷到10，10到20，20到30，30到正无穷
var threshold = d3.scale.threshold().domain([10,20,30]).range(["red","green","blue","black"]);console.log( threshold(5) );                   //输出red
console.log( threshold(15) );                 //输出green
console.log( threshold(25) );                 //输出blue
console.log( threshold(35) );                 //输出black

console.log( threshold.invertExtent("red") );                   //输出[undefined,10]
console.log( threshold.invertExtent("green") );                 //输出[10,20]
console.log( threshold.invertExtent("blue") );                  //输出[20,30]
console.log( threshold.invertExtent("black") );                 //输出[30,undefined]