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export function groupBy(groupFn, list){  if (arguments.length === 1) return _list => groupBy(groupFn, _list)
  const result = {}  for (let i = 0; i < list.length; i++){    const item = list[ i ]    const key = groupFn(item)
    if (!result[ key ]){      result[ key ] = []    }
    result[ key ].push(item)  }
  return result}