alternative answer for question http://stackoverflow.com/questions/40516763/javascript-adding-0-values-to-arrays-of-different-sizes/41176699

sof.js

let isUniq = (value, index, self) => 
  self.indexOf(value) === index;

let toLetters = (result, item) => 
  [...result, ...item.bars.map(b => b.label)];

let labels = groups
  .reduce(toLetters, [])
  .filter(isUniq)
  .sort()


let newgroups = groups.map(item  => {
  let dontHasLabel = (label) =>
    !item.bars.some(b => b.label === l);
  
  let toZeroBar = (label) => 
    ({label, value:0});

  let zeroValues = labels.filter(dontHasLabel).map(toZeroBar);
  
  item.bars = [...item.bars, ...zeroValues];
  
  return item;
});