I have issues creating a logarithmic scale in d3. The scale works fine if it is set to linear.
This works:
var myLinScale = d3.scale.linear()
.domain([0, 100])
.range([50, 1150]);
console.log(myLinScale(71)); //output = 831
However, this doesn't work:
var myLogScale = d3.scale.log()
.domain([0, 100])
.range([50, 1150]);
console.log(myLogScale(71)); //output = NaN
What is wrong with the logarithmic scale?
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).
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.
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>
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>
Original answer (for D3 v3)
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>
In the above demo I'm using 1e-6
, which is 0.000001
.
Explanation:
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.
In pure JavaScript:
console.log("Log of 0 is: " + Math.log(0))
Thus, in JavaScript, log(0)
is negative infinity, or minus infinity.
That being said, according to the API:
a log scale must have either an exclusively-positive or exclusively-negative domain; the domain must not include or cross zero. (emphasis mine)