How do I filter a tree by a non-existing property in parent-CodePudding

I have a structure like this:

const tree = [
  {
    "a": "1",
    "children": [
      {
        "a": "11",
        "children": [
            { "a": "111", "p": "me" }, 
            { "a": "112" }
        ]
      },
      { "a": "111", "p": "me" }
    ]
  },
  { "a": "2" },
  { "text": "3", "p": "me" }
]

And I'm trying to filter the tree by p: "me", however, I keep bumping into the parent and can't get past it. My desired output is something in these lines:

const res = filter(tree, "p", "me")
console.log(res)
/*
[
  {
    "a": "1",
    "children": [
      {
        "a": "11",
        "children": [
            { "a": "111", "p": "me" }, 
        ]
      },
      { "a": "111", "p": "me" }
    ]
  },
  { "text": "3", "p": "me" }
]
*/

I've tried other solutions and tweak them (like this one), but I'm struggling

CodePudding user response：

Check my comments in code.

The trick is to know when to go into recursion to go deeper in the tree and when to return the true/false for the JS filter() method.

const tree = [
  {
    "a": "1",
    "children": [
      {
        "a": "11",
        "children": [
            { "a": "111", "p": "me" }, 
            { "a": "112" }
        ]
      },
      { "a": "111", "p": "me" }
    ]
  },
  { "a": "2" },
  { "text": "3", "p": "me" }
]

const filter = (array, property, value) => {
  // Filter an array...
  return array.filter((object) => {
    // If an object of the array has a 'children'
    if(object.children){
      // It goes into recursion to set the filtered 'children'
      object.children = filter(object.children, property, value)
      // Then returns true if the children array is not empty
      return object.children.length
    }
    // If the object has a 'p' === 'me' (passed as arguments), it returns true (or false to discards the object)
    return object[property] === value
  })
}

console.log(filter(tree, "p", "me"))

CodePudding user response：

We can build this atop a reusable deep-filtering function, just passing it a predicate to say whether we're keeping an object. This one uses a deepFilter function that I have lying around my virtual toolbox:

const deepFilter = (pred) => (xs) =>
  xs .flatMap (({children = [], ...rest}, _, __, kids = deepFilter (pred) (children)) =>
    pred (rest) || kids.length
      ? [{...rest, ...(kids.length ? {children: kids} : {})}]
      : []
  )

const keepProp = (name, value) =>
  deepFilter (x => x [name] == value)

const tree= [{a: "1", children: [{a: "11", children: [{a: "111", p:"me"}, {a: "112"}]}, {a: "111", p: "me"}]}, {a: "2"}, {text: "3", p: "me"}]

console .log (keepProp ('p', 'me') (tree))

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

Note that no objects are harmed in the use of this function. It treats your data as immutable.