Pivot an array of objects by key

Accumulate values by key from an array of objects (key/value mappings):

records = [
  { a: 10, b: 20, c: 30 }, 
  { a: 11, b: 21 }, 
  { a: 12, b: 22, c: 32, d: 42 }
]

pivoted = pivot(records)

Expected result:

pivoted = { 
  a: [ 10, 11, 12 ], 
  b: [ 20, 21, 22 ], 
  c: [ 30, 32 ], 
  d: [ 42 ] 
}