Javascript recursive function to change object structure

Question

I want to convert an object structure to a structure which the Json-rules-engine can use.

I have this array as input, where A, B, C, D and E are some arbitrary condition.

INPUT

[
  {
    operator: 'any',
    conditions: [
      {
        operator: 'all',
        conditions: [
          { operator: 'all', conditions: [ A, B ] },
          { operator: 'any', conditions: [ C, D ] }
        ]
      },
      E
    ]
  }
]

I want to reach an output in the following structure:

{
    any: [E,
        {
            all: [{
                all: [A, B],
                any: [C, D]
            }],
        }
    ]
}

I am pretty sure that I need a recursive function for this. I have already tried the following. The problem here is that the output is overwritten, while I want it to be expanded when the recursive function reaches deeper levels of the array.

recursive(input, output) {
    input.forEach((el) => {
      if (typeof el !== "number") {
        output[el.operator] = el.conditions
        this.recursive(el.conditions, output);
      }
    });
  }

Thanks in advance!

@epascarello What do you mean? I have modified the object to make it more clear. The conditions A B C D E are actually objects, but that would make it unclear. — P.Yntema
– P.Yntema, Commented Jan 20, 2021 at 16:46
What is the outer array in the input for? What would be the result for [{op: 'any', conds: [A, B]}, {op: 'any', conds: [B, C]}]? — Scott Sauyet
– Scott Sauyet, Commented Jan 20, 2021 at 16:49

Scott Sauyet · Accepted Answer · 2021-01-20 18:35:10Z

2

Here's a very simple function designed to transform one element of your input. As mentioned in the comments, I don't understand what the outer array in the input is for, and why there is no corresponding one in the output. But if you need to, you can just map this function over the input. (If they are supposed to fold into a single object, I think you need to explain how you would like that done.)

const transform = (x) => 
  Object (x) === x && 'operator' in x
    ? {[x .operator]: (x .conditions || []) .map (transform)}
    : x

const input = [{operator: 'any', conditions: [{operator: 'all', conditions: [{operator: 'all', conditions: ['A', 'B']}, {operator: 'any', conditions: ['C', 'D']}]}, 'E']}]

console .log (transform (input [0]))

.as-console-wrapper {max-height: 100% !important; top: 0}

It also does not change the condition order, which your output seems to want. (Because E comes first.) If you do want to reorder them, what's the requirement?

answered Jan 20, 2021 at 18:35

Scott Sauyet

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4 Comments

Mulan Over a year ago

Object (x) === x && 'operator' in x is now the verbose way of saying x?.operator :D beautiful arrow expression.

Scott Sauyet Over a year ago

@Thankyou: They're not entirely equivalent (think {operator: 0}) although that would probably be fine for this case. Mostly, I just need to upgrade the REPL I use for these problems to support it. Someday.

Mulan Over a year ago

Which repl are you using?

Scott Sauyet Over a year ago

@Thankyou: ramdajs.com/repl, which means that changing it really falls to me (or hopefully someone else on the team who remembers how it works!)

Mulan · Accepted Answer · 2021-01-20 23:22:13Z

Adding my solution to the mix of other answers here. This transform does a simple type analysis on the input t and has excellent readability -

function transform (t)
{ switch (t?.constructor)
  { case Object:
      return { [t.operator]: transform(t.conditions) }
    case Array:
      return t.map(transform)
    default:
      return t
  }
}

const input =
  [{operator: 'any', conditions: [{operator: 'all', conditions: [{operator: 'all', conditions: ['A', 'B']}, {operator: 'any', conditions: ['C', 'D']}]}, 'E']}]

console.log(transform(input))

Because input is wrapped in an array, [...], the output is also wrapped -

[
  {
    "any": [
      {
        "all": [
          {
            "all": [
              "A",
              "B"
            ]
          },
          {
            "any": [
              "C",
              "D"
            ]
          }
        ]
      },
      "E"
    ]
  }
]

If you'd like to strip the outer array, you can either unwrap the input, transform(input[0]) or unwrap the output, transform(input)[0].

Jamiec · Accepted Answer · 2021-01-20 16:50:54Z

1

I split this into two methods as I think it reads a bit easier, but you could combine them if you wanted. Note that A,B etc I needed to make a string to make this runnable.

const convertObj = (obj) => {
  return {[obj.operator]: convertConditions(obj.conditions)}
}

const convertConditions = (arr) => {
  return arr.map(i => {
    if(typeof i == "string") {
      return i
    }else{
      return convertObj(i);
    }
  })
}

Live example:

var input = [{
  operator: 'any',
  conditions: [{
      operator: 'all',
      conditions: [{
          operator: 'all',
          conditions: ["A", "B"]
        },
        {
          operator: 'any',
          conditions: ["C", "D"]
        }
      ]
    },
    "E"
  ]
}]

const convertObj = (obj) => {
  return {[obj.operator]: convertConditions(obj.conditions)}
}

const convertConditions = (arr) => {
  return arr.map(i => {
    if(typeof i == "string") {
      return i
    }else{
      return convertObj(i);
    }
  })
}

var result = convertObj(input[0]);

console.log(result);

answered Jan 20, 2021 at 16:50

Jamiec

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2 Comments

P.Yntema Over a year ago

This seems to be working for me, but it looks very similar to my solution. Would it be possible to do it within one method? Or was I doing it completely wrong?

Scott Sauyet Over a year ago

@P.Yntema: Mutual recursion is often cleaner than trying to squeeze everything into one function. While it could be done here, it would to my mind be less clear. (Alternatively, see my solution, which does this in a single function, but doesn't try to handle the mysterious outer array. Edit: Oh, neither does this one)

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