acordeon.js

var e = [
  [["0a"],["0e"],["0i"],["0o"],["0u"]],
  [["1a"],["1e"],["1i"],["1o"],["1u"]],
  [["2a"],["2e"],["2i"],["2o"],["2u"]],
  [["3a"],["3e"],["3i"],["3o"],["3u"]],
  [["4a"],["4e"],["4i"],["4o"],["4u"]]
]

const yZip = e.reduce((a, b, i) => {
  lst = a.slice(-1)[0]
  if (i % 3) {
      lst.forEach((e, i) => e.push(...b[i]))
  } else {
      a.push(b)
  }
  return a
}, [])

const xZip = e.map(
  e => e.reduce((a, b, i) => {
    lst = a.slice(-1)[0]
    if (i % 3) {
      lst.push(...b)
    } else {
      a.push(b)
    }
    return a
  }, [])
)