Removing null at beginning and end of array

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Looking for an algorithm that will remove null that occurs at the beginning and end of the array and nothing in between that is O(n)

For example:

[null, null, 1, 2, 3, null, null, null] -> [1, 2, 3]

[null, null, 1, 2, null, 3, null, null, null] -> [1, 2, null, 3]

[1, null, 2, 3, null, 4, null, null, null] -> [1, null, 2, 3, null, 4]

[null, null, 2, 3, null, 4, null, null, 5] -> [2, 3, null, 4, null, null, 5]

Bit chunky but works.

const tests = [[null, null, 1, 2, 3, null, null, null],
[null, null, 1, 2, null, 3, null, null, null],
[1, null, 2, 3, null, 4, null, null, null],
[null, null, 2, 3, null, 4, null, null, 5]];

const strip = (arr) => {
  const end = arr.length-(arr.reverse().findIndex(a => a != null));
  const start = arr.reverse().findIndex(a => a != null);
  return arr.slice(start, end);
};

tests.forEach(a => console.log(strip(a)));

How to Remove Empty Values from an Array in PHP, How to remove the last element from an array in PHP � How to delete an element from an array in PHP � Previous Page Next Page. Advertisements. The array methods push() and pop() work on the the end of an array. The terms push() and pop() come from the idea of a stack in memory from the early days of microprocessors. This implements the idea of a Last-In-First-Out data structure (LIFO). The push() method will ADD an element to the array and the pop() method will remove one.

Here's a relatively small solution that should be O(n). You do one pass to get the start and end positions of your array and then another pass when you do a .slice.

const trimmer = arr => {
  const positions = arr.reduce((acc, el, i) => {
    if(el !== null) {
      acc[1] = i + 1;
      if (acc[0] === undefined) acc[0] = i;
    }
    return acc;
  }, [undefined, undefined]);
  return arr.slice(...positions);
}

console.log(trimmer([null, null, 1, 2, 3, null, null, null]));
console.log(trimmer([null, null, 1, 2, null, 3, null, null, null]));
console.log(trimmer([1, null, 2, 3, null, 4, null, null, null]));
console.log(trimmer([null, null, 2, 3, null, 4, null, null, 5]));

JavaScript array: Remove null, 0, blank, false, undefined and NaN , home Front End HTML CSS JavaScript HTML5 Schema.org php.js Twitter Sample array: [NaN, 0, 15, false, -22, '',undefined, 47, null] So, we need to create a String array first and add some elements to it. Remember to add one or more null values too. As our main aim is to create a Java program to remove null values from a String array. how to convert Object array to String array in java. Remove null value from String array in Java. In the below example I will create a String

Just have two indexes moving from both ends, then call slice.

const tests = [
    [0, 0, 1, 2, 3, 0, 0, 0, 0],
    [0, 0, 1, 2, 0, 3, 0, 0, 0],
    [1, 0, 2, 3, 0, 4, 0, 0, 0],
    [0, 0, 2, 3, 0, 4, 0, 0, 5],
    [0, 0, 8, 0, 0, 0],
    [1, 2, 3],
    [0, 0, 0],
    []

];


function trim(a, value) {
    let s, e, len = a.length;

    for (s = 0;       s < len && a[s] === value; s++) ;
    for (e = len - 1; s < e   && a[e] === value; e--) ;

    return a.slice(s, e + 1);
}

for (let t of tests)
    console.log(JSON.stringify(t), '->', JSON.stringify(trim(t, 0)))

Remove Null Elements From Array With Javascript (like Ruby Array , For those coming from Ruby, Javascript has no builtin method like Ruby's Array# compact. This method removes nil items from a an array. Following program creates an array with null values. Convert it a list with not-null values only and then get the array of that list.Exampleimport java.util.Arr

Program to remove empty array elements in PHP, Python - Initialize empty array of given length � JavaScript TypeError - Reduce of empty array with no initial value � jQuery | Remove Elements� Removing Elements from End of a JavaScript Array JavaScript Array elements can be removed from the end of an array by setting the length property to a value less than the current value. Any element whose index is greater than or equal to the new length will be removed.

JavaScript, In order to remove empty elements from an array, filter() method is used. Example: This example is removing undefined, null and empty elements from the array. JavaScript | Add new elements at the beginning of an array� The index at which to start changing the array. If greater than the length of the array, start will be set to the length of the array. In this case, no element will be deleted but the method will behave as an adding function, adding as many element as item[n*] provided. If negative, it will begin that many elements from the end of the array.

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Comments
  • You can identify the positions of the first and last elements with one scan, so O(n), and then just Array.splice, and I assume that's O(n) too, if not better internally.
  • Oops, I meant Array.slice, to return a new copy of the trimmed array. But then maybe splice is what you wanted.
  • I don't think it's worth reversing the array twice just so you can use findIndex - that's too much work. It would be easier to just scan with for(let i = arr.length - 1; i >= 0; --i) I'd think.
  • Single loop, no reverse and minimum scan in second example.
  • Nice. I'm not sure there's any benefit to merging the two scan loops, and I'd guess it won't cope with an input array of all nulls.
  • Assume empty array is desired for all nulls?
  • I'd guess so? But now you've run into the danger of doing both loops together: x and i meeting isn't the limit. Try [null, 1, null, null, null, null, null]: x and i will meet in the middle before you find the right value of end and you'll assume it's empty. And if the length is even then x and i will cross and not equal each other anyway.