add descending sorter function

Author: etpinard

src/lib/index.js

@@ -31,6 +31,7 @@ lib.parseDate = datesModule.parseDate;
 var searchModule = require('./search');
 lib.findBin = searchModule.findBin;
 lib.sorterAsc = searchModule.sorterAsc;
+lib.sorterDec = searchModule.sorterDes;
 lib.distinctVals = searchModule.distinctVals;
 lib.roundUp = searchModule.roundUp;
 

src/lib/search.js

@@ -56,6 +56,7 @@ function greaterThan(a, b) { return a > b; }
 function greaterOrEqual(a, b) { return a >= b; }
 
 exports.sorterAsc = function(a, b) { return a - b; };
+exports.sorterDes = function(a, b) { return b - a; };
 
 /**
  * find distinct values in an array, lumping together ones that appear to