Transform an array by mapping it to remove any empty elements

Question

Transform an array by mapping it to remove any empty elements

Supplied with:

let input = [0, 1, 2,,,,,7]

I am aiming for:

let output = [, 1, 22, 333, 4444, 55555, 666666, 7777777]

(meaning each value is equal to the key times the key)

How can I perform a map operation (or similar) on the input even if it contains empty values?
When using input.map(), the resulting array will be [, 1, 22,,,,,7777777] since map naturally skips over empty entries. The data could vary from strings, objects, numbers, etc., but for simplicity, numbers are used in this example.

javascript arrays

Answer 1

Answer №1

To ensure all indexes are iterated over, including empty ones, it is recommended to fill the array before applying a mapping function.

let result = input.fill().map((_,index)=>{/*...*/});

Similarly, the mapping function provided as the second argument to Array.from can be utilized for this purpose.

let result = Array.from({length: input.length}, (_, index)=>{/*...*/});

Spread syntax does not ignore empty slots, so creating a copy of the array with spread syntax and using map on it can be beneficial. This approach also ensures that the elements at each index are accessible.

let result = [...input].map((elem, idx)=>{/*...*/});

Answer 2

To ensure all indexes are iterated over, including empty ones, it is recommended to fill the array before applying a mapping function.

let result = input.fill().map((_,index)=>{/*...*/});

Similarly, the mapping function provided as the second argument to Array.from can be utilized for this purpose.

let result = Array.from({length: input.length}, (_, index)=>{/*...*/});

Spread syntax does not ignore empty slots, so creating a copy of the array with spread syntax and using map on it can be beneficial. This approach also ensures that the elements at each index are accessible.

let result = [...input].map((elem, idx)=>{/*...*/});

Answer 3

Answer №2

map() function in JavaScript cannot handle empty values according to w3schools

The map() method does not process array elements that are empty.

To work around this limitation, you can either use a for-loop to iterate through the array:

out = [];
for (var i = 0; i < input.length; i++) {
    var item = input[i];
    if (item != null)
        out[i] = item.toString().repeat(item);
}

Alternatively, you can create a custom functor called mapx():

Array.prototype.mapx = function(fn) {
    var out = [];
    for (var i = 0; i < this.length; i++) {
        var item = this[i];
        // if (item == null) item = sherlockHolmesKnow();
        out[i] = fn(item, i);
    }
    return out;
};

and then apply it on the input array like this:

input.mapx( (val, index) => (val == null ? null : (val+'').repeat(val)) )

This will result in an output of ["", "1", "22", null, null, null, null, "7777777"].

We'll leave out the artificial intelligence aspect of guessing numbers in the empty slots for now.

Answer 4

map() function in JavaScript cannot handle empty values according to w3schools

The map() method does not process array elements that are empty.

To work around this limitation, you can either use a for-loop to iterate through the array:

out = [];
for (var i = 0; i < input.length; i++) {
    var item = input[i];
    if (item != null)
        out[i] = item.toString().repeat(item);
}

Alternatively, you can create a custom functor called mapx():

Array.prototype.mapx = function(fn) {
    var out = [];
    for (var i = 0; i < this.length; i++) {
        var item = this[i];
        // if (item == null) item = sherlockHolmesKnow();
        out[i] = fn(item, i);
    }
    return out;
};

and then apply it on the input array like this:

input.mapx( (val, index) => (val == null ? null : (val+'').repeat(val)) )

This will result in an output of ["", "1", "22", null, null, null, null, "7777777"].

We'll leave out the artificial intelligence aspect of guessing numbers in the empty slots for now.

Answer 5

Answer №3

Here is an alternative method that may seem lengthy but it gets the job done. By using a for loop, you can iterate through null values within an array.

arr=[0, 1, 2,,,,,7]
res=[]
f=false
for(let i=0;i<arr.length-1;i++){
  if(arr[i]!=undefined){
      res.push(Number(String(arr[i]).repeat(arr[i]))
  }
  if(arr[i]==undefined&&f==false){
    n = arr[i-1]  
    f=true
    res.push(Number(String(n+1).repeat(n+1)))
  }
  if(f==true && arr[i]==undefined){
     n = Number(res[res.length-1].toString().charAt(0))+1
      res.push(Number(String(n).repeat(n)))
    }
}
console.log(res)

Answer 6

Here is an alternative method that may seem lengthy but it gets the job done. By using a for loop, you can iterate through null values within an array.

arr=[0, 1, 2,,,,,7]
res=[]
f=false
for(let i=0;i<arr.length-1;i++){
  if(arr[i]!=undefined){
      res.push(Number(String(arr[i]).repeat(arr[i]))
  }
  if(arr[i]==undefined&&f==false){
    n = arr[i-1]  
    f=true
    res.push(Number(String(n+1).repeat(n+1)))
  }
  if(f==true && arr[i]==undefined){
     n = Number(res[res.length-1].toString().charAt(0))+1
      res.push(Number(String(n).repeat(n)))
    }
}
console.log(res)

Transform an array by mapping it to remove any empty elements

Answer №1

Answer №2

Answer №3

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