对数刻度返回NaN [英] Logarithmic scale returns NaN

问题描述

我在d3中创建对数刻度时遇到问题.如果将比例尺设置为线性，则效果很好.

I have issues creating a logarithmic scale in d3. The scale works fine if it is set to linear.

这有效:

var myLinScale = d3.scale.linear()
      .domain([0, 100])
      .range([50, 1150]);

console.log(myLinScale(71)); //output = 831

但是，这不起作用:

var myLogScale = d3.scale.log()
      .domain([0, 100])
      .range([50, 1150]);

console.log(myLogScale(71)); //output = NaN

对数刻度有什么问题?

推荐答案

新解决方案(使用D3 v5.8)

经过两年多的时间，这个问题终于有了一个基于D3的答案，并不像我在原始答案中所做的那样建议从域中删除0(见下文).

New solution (using D3 v5.8)

After more than 2 years this question finally has a D3-based answer that doesn't suggest removing 0 from the domain, as I did in my original answer (see below).

由于新的符号比例在D3 v5.8中，基于通过对称日志转换，该域允许为0.

This is possible due to the new Symlog scale in D3 v5.8, based on a by-symmetric log transformation, which allows 0 in the domain.

因此，请使用您的域和范围而无需进行任何修改:

So, using your domain and range without any modification:

var myLogScale = d3.scaleSymlog()
  .domain([0, 100])
  .range([50, 1150]);

console.log(myLogScale(71));

<script src="https://d3js.org/d3.v5.min.js"></script>

甚至更短，使用D3 v5.8中的新比例尺构造器:

Or even shorter, with the new scale constructors in D3 v5.8:

var myLogScale = d3.scaleSymlog([0, 100], [50, 1150]);

console.log(myLogScale(71));

<script src="https://d3js.org/d3.v5.min.js"></script>

更改您的域，使其不包含或不为零:

Change your domain so it doesn't include or cross zero:

var myLogScale = d3.scale.log()
      .domain([1e-6, 100])//domain doesn't include zero now
      .range([50, 1150]);

console.log(myLogScale(71));

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

在上面的演示中，我使用的是1e-6，即0.000001.

In the above demo I'm using 1e-6, which is 0.000001.

说明:

零的对数未定义(或未定义).例如，在以10为底的log(0)是一个数字x，因此加到x的幂的10就是零...那个数字当然不存在.但是，当我们从正方向接近零时的极限是负无穷大.

The logarithm of zero is undefined (or not defined). In base 10, for instance, log(0) is a number x so that 10 raised to the power of x is zero... that number, of course, doesn't exist. The limit, however, when we approach zero from the positive side is minus infinity.

在纯JavaScript中:

In pure JavaScript:

console.log("Log of 0 is: " + Math.log(0))

因此，在JavaScript中，log(0)是负无穷大或负无穷大.

Thus, in JavaScript, log(0) is negative infinity, or minus infinity.

话虽如此，根据 API :

对数标度必须具有一个专有的正值或专有的负值域；该域不得包含零或跨越零. (强调我的)

a log scale must have either an exclusively-positive or exclusively-negative domain; the domain must not include or cross zero. (emphasis mine)

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