CODEWITHSUNDEEP
javascriptstringreplace
user10109
user10109

Reputation: 121

What is the best method to swap words in a string

Given the following string how would I swap the words right and left.

i.e. change

let str = JSON.stringify({
  val: 4,
  right: {
    val: 7,
    right: { val: 9, right: null, left: null },
    left: { val: 6, right: null, left: null },
  },
  left: {
    val: 2,
    right: { val: 3, right: null, left: null },
    left: { val: 1, right: null, left: null },
  },
}, null, 2);

str = str.replace((/"left"/g), o => { return "right1" }); 
str = str.replace((/"right"/g), o => { return "left1" });

console.log(); 
console.log(str); 

str = str.replace((/"right1"/g), o => { return "right" });

console.log(); 
console.log(str); 

str = str.replace((/"left1"/g), o => { return "left" });

I'm thinking of using str.replace().

Upvotes: 0

Views: 1180

Answers (5)

The fourth bird
The fourth bird

Reputation: 163577

The first parameter of the function that you can pass to replace is the match.

You could update your code to use an alternation to match either "left" or "right" and flip the values.

(?:left|right)

let replaced = str.replace(/(?:left|right)/g, o => {
  return o === "left" ? "right" : "left";
});

Note that using this regex you would also match "left" in "alefta". If you want to match left or right only you could use a word boundary \b:

\b(?:left|right)\b

let str = JSON.stringify({
  val: 4,
  right: {
    val: 7,
    right: {
      val: 9,
      right: null,
      left: null
    },
    left: {
      val: 6,
      right: null,
      left: null
    },
  },
  left: {
    val: 2,
    right: {
      val: 3,
      right: null,
      left: null
    },
    left: {
      val: 1,
      right: null,
      left: null
    },
  },
}, null, 2);

let replaced = str.replace(/(?:left|right)/g, o => {
  return o === "left" ? "right" : "left";
});

console.log(replaced);

Upvotes: 1

Matt Burland
Matt Burland

Reputation: 45155

Don't stringify (or if starting from a string, parse it first). Work with the object itself and you can easily write a recursive function to do this:

var original = {
  val: 4,
  right: {
    val: 7,
    right: { val: 9, right: null, left: null },
    left: { val: 6, right: null, left: null },
  },
  left: {
    val: 2,
    right: { val: 3, right: null, left: null },
    left: { val: 1, right: null, left: null },
  },
};

function swapLR(obj) {
    if (!obj || (obj.left == null && obj.right == null)) {
        return obj;
    }
    var tmp = swapLR(obj.left);
    obj.left = swapLR(obj.right);
    obj.right = tmp;
    return obj;
}

console.log(original);
console.log(swapLR(original));

You can then stringify it back at the end if you need to.

Upvotes: 1

Patrick Evans
Patrick Evans

Reputation: 42746

Don't use string manipulation, keep/parse as object and swap the properties:

function swapLeftRight(obj){
  //use object deconstruction to create left and right variables, 
  //and assign them to the opposite name
  let {left:right, right:left} = obj;
  //Assign the new values
  obj.left = left, obj.right = right;
  //Use recursion if the properties are not null
  if(obj.left) swapLeftRight(obj.left);
  if(obj.right) swapLeftRight(obj.right);
}
var data = {
  val: 4,
  right: {
    val: 7,
    right: { val: 9, right: null, left: null },
    left: { val: 6, right: null, left: null },
  },
  left: {
    val: 2,
    right: { val: 3, right: null, left: null },
    left: { val: 1, right: null, left: null },
  }
};
swapLeftRight(data);
console.log(data);

Upvotes: 1

m0meni
m0meni

Reputation: 16445

The simplest way is to use a placeholder, and then replace the placeholder,

let str = JSON.stringify({
  val: 4,
  right: {
    val: 7,
    right: { val: 9, right: null, left: null },
    left: { val: 6, right: null, left: null },
  },
  left: {
    val: 2,
    right: { val: 3, right: null, left: null },
    left: { val: 1, right: null, left: null },
  },
}, null, 2);

let newStr = str
  .replace('right', '$')
  .replace('left', 'right')
  .replace('$', 'left')

console.log(newStr)

Alternatively, you can parse the JSON, and recursively swap nodes because you actually have a binary tree on your hands.

Upvotes: 0

Lece
Lece

Reputation: 2377

If you want to use replace, use a temporary value:

let str = '{"val":4,"right":{"val":7,"right":{"val":9,"right":null,"left":null},"left":{"val":6,"right":null,"left":null}},"left":{"val":2,"right":{"val":3,"right":null,"left":null},"left":{"val":1,"right":null,"left":null}}}';

function swap() {
  str = str.replace(/right/g, "temp");
  str = str.replace(/left/g, "right");
  str = str.replace(/temp/g, "left");
  console.log(str);
}

swap();

Upvotes: 0

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