Sort doubly linked list by next id Ramda.js

Question

I want to sort doubly linked list by next_id value.

My DLL:

const dll = [
  {id: '22', prev_id: '41', next_id: '45'},
  {id: '45', prev_id: '22', next_id: null},
  {id: '41', prev_id: '14', next_id: '22'},
  {id: '14', prev_id: null, next_id: '41'},
]

As a result:

const dll_result = [
  {id: '14', prev_id: null, next_id: '41'}, // next item - 41
  {id: '41', prev_id: '14', next_id: '22'}, // next item - 22
  {id: '22', prev_id: '41', next_id: '45'}, // next item - 45
  {id: '45', prev_id: '22', next_id: null},
]

I understand that it may not make sense to sort the DLL, but in my case I need to sequentially visualize the data from the array using next_id.

P.S. It would be nice to know even a native solution, and then I could try to convert to Ramda.js myself

Answer 1

Create an index of items by id, find the 1st item (prev_id === null), and then iterate with a while loop, and push the current object into the result array:

const findStart = R.find(R.propEq('prev_id', null))
const indexById = R.indexBy(R.prop('id'))

const sortByNextId = arr => {
  const index = indexById(arr)
  let current = findStart(arr)
  
  const sorted = []
  
  while(current) {
    sorted.push(current)
    current = index[current.next_id]
  }
  
  return sorted
}

const dll = [
  {id: '22', prev_id: '41', next_id: '45'},
  {id: '45', prev_id: '22', next_id: null},
  {id: '41', prev_id: '14', next_id: '22'},
  {id: '14', prev_id: null, next_id: '41'},
]

const result = sortByNextId(dll)

console.log(result)

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