src/Utl.js
function runningMap(a, fn, init) {
  return a.map(v => init = fn(v, init));
}
function runningMap(a, fn, init) {
  return a.map(v => init = fn(v, init));
}
function runningMap ( a , fn , init ) { return a . map ( v => init = fn ( v , init ) ) ; }
Create an array of running totals, etc.
Create an array of running totals etc .