Sort an array so that null values always come last
JavascriptJavascript Problem Overview
I need to sort an array of strings, but I need it so that null is always last. For example, the array:
var arr = [a, b, null, d, null]
When sorted ascending I need it to be sorted like [a, b, d, null, null]
and when sorted descending I need it to be sorted like [d, b, a, null, null]
.
Is this possible? I tried the solution found below but it's not quite what I need.
Javascript Solutions
Solution 1 - Javascript
Check out .sort()
and do it with custom sorting.
Example
function alphabetically(ascending) {
return function (a, b) {
// equal items sort equally
if (a === b) {
return 0;
}
// nulls sort after anything else
else if (a === null) {
return 1;
}
else if (b === null) {
return -1;
}
// otherwise, if we're ascending, lowest sorts first
else if (ascending) {
return a < b ? -1 : 1;
}
// if descending, highest sorts first
else {
return a < b ? 1 : -1;
}
};
}
var arr = [null, 'a', 'b', null, 'd'];
console.log(arr.sort(alphabetically(true)));
console.log(arr.sort(alphabetically(false)));
Solution 2 - Javascript
Use a custom compare function that discriminates against null
values:
arr.sort(function(a, b) {
return (a===null)-(b===null) || +(a>b)||-(a<b);
});
For descending order of the non-null values, just swap a
and b
in the direct comparison:
arr.sort(function(a, b) {
return (a===null)-(b===null) || -(a>b)||+(a<b);
});
Solution 3 - Javascript
Ascending
arr.sort((a, b) => (a != null ? a : Infinity) - (b != null ? b : Infinity))
Descending
arr.sort((a, b) => (b != null ? b : -Infinity) - (a != null ? a : -Infinity))
(For descending order if you don't have negative values in the array, I recommend to use 0 instead of -Infinity)
Solution 4 - Javascript
The simplest approach is to handle null
first, then deal with non-null cases based on the desired order:
function sortnull(arr, ascending) {
// default to ascending
if (typeof(ascending) === "undefined")
ascending = true;
const multiplier = ascending ? 1 : -1;
const sorter = function(a, b) {
if (a === b) // identical? return 0
return 0;
else if (a === null) // a is null? last
return 1;
else if (b === null) // b is null? last
return -1;
else // compare, negate if descending
return a.localeCompare(b) * multiplier;
}
return arr.sort(sorter);
}
const arr = ["a", "b", null, "d", null];
console.log(sortnull(arr)); // ascending ["a", "b", "d", null, null]
console.log(sortnull(arr, true)); // ascending ["a", "b", "d", null, null]
console.log(sortnull(arr, false)); // descending ["d", "b", "a", null, null]
Solution 5 - Javascript
If you need natural sorting for numbers, or any of the options provided by Collator
(including speed enhancements and respecting locale), try this approach, based off of Paul Roub's solution, cleaned up a bit. We almost always use numeric sorting, hence the defaults...
If you are not a Typescript fan, just strip off the :type
specs or copy from the snippet.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Collator
const naturalCollator = new Intl.Collator(undefined, {numeric: true, sensitivity: 'base'});
const alphabeticCollator = new Intl.Collator(undefined, {});
function nullSort(descending: boolean = false, alphabetic: boolean = false) {
return function (a: any, b: any): number {
if (a === b) {
return 0;
}
if (a === null) {
return 1;
}
if (b === null) {
return -1;
}
let ret
if (alphabetic) {
ret = alphabeticCollator.compare(a, b)
} else {
ret = naturalCollator.compare(a, b)
}
if (descending) {
ret = -ret
}
return ret
};
}
Use it like this.
// numeric, ascending (default)
myList.sort(nullSort());
// alphabetic, descending
myList.sort(nullSort(true, true));
You can modify the factory method to take a collator instead, for greater flexibility.
function nullSort(descending: boolean = false, collator: Collator = naturalCollator)
Working Snippet
const naturalCollator = new Intl.Collator(undefined, {
numeric: true,
sensitivity: 'base'
});
const alphabeticCollator = new Intl.Collator(undefined, {});
function nullSort(descending = false, alphabetic = false) {
return function(a, b) {
if (a === b) {
return 0;
}
if (a === null) {
return 1;
}
if (b === null) {
return -1;
}
let ret
if (alphabetic) {
ret = alphabeticCollator.compare(a, b)
} else {
ret = naturalCollator.compare(a, b)
}
if (descending) {
ret = -ret
}
return ret
};
}
const items = [null, 10, 1, 100, null, 'hello', .1, null]
console.log(items.sort(nullSort()));
Solution 6 - Javascript
like this, note: this will only push the null's to the back
var arr = ["a", null, "b"];
var arrSor = [];
arr.forEach(function (el) {
if (el === null) {
arrSor.push(el);
} else {
arrSor.unshift(el);
}
});
Solution 7 - Javascript
Do it like:
var arr = [a, b, null, d, null]
foreach ($arr as $key => $value) {
if($value == null)
unset($arr[$key]);
$arr[] = $value;
}
// rebuild array index
$arr = array_values($arr);
echo '<pre>';print_r($arr);die;
Solution 8 - Javascript
I am sorting objects with a custom index and this works for me. I am not wanting to change the original array and it is important to keep the null indexes where they are.
let sorted = [...array].sort((a, b) => {
if (!a || !b) return 0;
else return a.CustomIndex - b.CustomIndex;
});
Solution 9 - Javascript
function sortNumsAsc(arr) {
if(arr === null || arr === []) {
return [];
}
else {
return arr.sort(function(a,b){return a-b});
//return newarr;
}
}
console.log(sortNumsAs([801, 19, 4, 5, -4, 85]))