I'm trying to slice an array at i 1 from the last null value.

The array is sorted to have null values first.

This is how it should behave:

[null, null, a, b, c] => [null, null, a, b]

[null, a, b, c] => [null, a, b]

[null, null] => [null, null]

I'm doing something like this but I'm not sure how to handle the null only arrays.

let newArray: = [];

for (let i = 0; i < array.length; i  ) {
  if (array[i] !== null) {
    newArray = array.slice(0, i   1);
    i  ;
  }
}

CodePudding user response：

There are some errors in your code that might be causing the unexpected behaviour.

• Since you have i inside of the for loop head you don't need to include it in the body.
• Since the second parameter of slice is non-inclusive, based on your test conditions you actually want to slice to i 2;

Full code:

function slice(array) {
    for (let i = 0; i < array.length; i  ) {
        if (array[i] !== null) return array.slice(0, i   2);
    }
    return array;
}

console.log(slice([null, null, 'a', 'b', 'c'])); // => [null, null, a, b]
console.log(slice([null, 'a', 'b', 'c'])); // => [null, a, b]
console.log(slice([null, null])); // => [null, null]

CodePudding user response：

You could take a closure over a counter for the next values and filter the array.

const
    slice = array => array.filter(
        (c => v => v === null || c && c--)
        (2)
    );

console.log(...slice([null, null, 'a', 'b', 'c', 'd', 'e'])); // [null, null, a, b]
console.log(...slice([null, null, 'a', 'b', 'c'])); // [null, null, a, b]
console.log(...slice([null, 'a', 'b', 'c'])); // [null, a, b]
console.log(...slice([null, null])); // [null, null]

CodePudding user response：

to remove null in array you can try

     var arr = [null, null, a, b, c];
     var temp = arr.filter(i=>i?true:false);
     arr = temp;

CodePudding user response：

const sliceAfterNull = (c, arr) => 
   arr.slice(0, arr.filter(v => v===null).length   c);

CodePudding user response：

Looks to me, from your examples, you only needed to sliced out an array without the last element of the array. You wanna change the first array with nulls, a, b and c to another with the same nulls, a and b.

[null, null, a, b, c] => [null, null, a, b]

Then if that's the case, why not just pop the array.

let arr = [null, null, a, b, c];
arr.pop();

arr is now [null, null, a, b];

For the special case in which only non null values should be removed, and thereby returning same array if it contains all nulls, you may just pop, inspect, and if null push back to original array again.

let arr = [null, null, a, b, c];
if(arr.pop() === null) arr.push(null);

And that's all!

You should please clarify what you mean by i 1. Sounds like you want to slice a new array with all nulls, and one element after it. But I cant answer to that because I'm not sure.