I have an array of objects as follows:
c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}]
I want to kind-of sort them by the objects having values first then objects with null.
What I tried is:
c.sort(function(b) { return b.a ? -1 : 1 })
OUTPUT
[{a: 2}, {a: 50}, {a: 1}, {a: 12}, {a: null}, {a: null}]
EXPECTED OUTPUT
[{a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}, {a: null}]
How can I achieve this?
This will put nulls and other falsy values to the end of the list:
c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}];
c.sort((x, y) => !!y.a - !!x.a);
console.log(c);However, since you don't really sort anything, you can just split the list into two parts an rejoin them:
c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}];
r = [
...c.filter(x => x.a !== null),
...c.filter(x => x.a === null)
]
console.log(r)This also doesn't rely on the sort function being stable.
filter option is much better than using sort in this use case, it avoids any stability problems.You could test the value. If null, then take the delta of the comparison.
var c = [{ a: null }, { a: 12 }, { a: 1 }, { a: 50 }, { a: 2 }, { a: null }];
c.sort(function (a, b) {
return (a.a === null) - (b.a === null);
});
console.log(c);.as-console-wrapper { max-height: 100% !important; top: 0; }For a stable sort, you could use sorting with map and use the indices as second sort option.
// the array to be sorted
var list = [{ a: null }, { a: 12 }, { a: 1 }, { a: 50 }, { a: 2 }, { a: null }];
// temporary array holds objects with position and sort-value
var mapped = list.map(function(el, i) {
return { index: i, value: el.a === null};
});
// sorting the mapped array containing the reduced values
mapped.sort(function(a, b) {
return a.value - b.value || a.index - b.index;
});
// container for the resulting order
var result = mapped.map(function(el){
return list[el.index];
});
console.log(result);.as-console-wrapper { max-height: 100% !important; top: 0; }
const c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}];
let result = [...c.filter(_=>_["a"]!==null),...c.filter(_=>_["a"]===null)];
console.log(result);Try with return !a.a - !b.a .valid object goes first
var c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}];
c.sort(function (a, b) {
return !a.a - !b.a
});
console.log(c);That way ?
c=[{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}];
c.sort(function(a,b){ return a.a===null ? 1:-1 })
console.log(c);
Edited
var c = [{
a: null
}, {
a: 12
}, {
a: 1
}, {
a: 50
}, {
a: 2
}, {
a: null
}];
c.sort(function(a, b) {
return (a.a !== null) ? 0 : 1;
});
console.log(c);Returning 0 in the sort function will keep the order as it is.
If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements.
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/sort
It is not perfect but still works,cheers!
var c = [{a: null}, {a: 12}, {a: 1}, {a: 50}, {a: 2}, {a: null}]
c.sort(function(object1,object2){
if(object1.a === null && object2.a !== null){return 1}
if([object1.a,object2.a].every((a)=>a === null) ||
[object1.a,object2.a].every((a)=>a !== null)
){return 0}
if(object1.a !== null && object2.a === null){return -1}
})
console.log(c);Here's a case of sorting a Date with null value at the end if exists:
userSortList = users.sort((a, b) => {
if (b.lastConnectionDate === null || a.lastConnectionDate) {
return -1
} else {
return (
new Date(b.lastConnectionDate) - new Date(a.lastConnectionDate)
)
}
})
aandbargument for comparison.