fix: Treat NaN as -infinity for sorting

* A couple of test cases with NaN's thrown in 

The first of these fails for me, I think its due to your sort method

* Treat NaN as -infinity for sorting

* Updated readme to make a note on NaN

README.md

@@ -37,6 +37,9 @@ var result = percentile(
 console.log(result); // 8
 
 ```
+## Notes
+
+Non-numeric (NaN) values are treated as the smallest values, Eg `percentile(50, [ 5, 2, NaN]) === 2`
 
 ## Author
 

lib/index.js

@@ -61,6 +61,9 @@ function percentile(p, list, fn) {
       b = fn(b);
     }
 
+    a = Number.isNaN(a) ? Number.NEGATIVE_INFINITY : a;
+    b = Number.isNaN(b) ? Number.NEGATIVE_INFINITY : b;
+
     if (a > b) return 1;
     if (a < b) return -1;
 

test/index.js

@@ -24,6 +24,8 @@ const stubsSimple = [
   { percentile: 75, list: shuffleArray(generateArraySimple(100)), result: 75 },
   { percentile: 100, list: shuffleArray(generateArraySimple(100)), result: 100 },
 
+  { percentile: 75, list: [NaN, NaN, 1, 100], result: 1 },
+  { percentile: 75, list: [1, 100, NaN, NaN], result: 1 },
   { percentile: 75, list: shuffleArray([].concat(generateArraySimple(100), generateArraySimple(30))), result: 68 }
 ];