[英]How to sort array by two properties - alphabetically but null values at the end?
[英]How to sort an array with null values
与该主题相关的问题很多,但我找不到适合我的案例的正确解决方案。
var arr = [a, b, null, d, null]
并使用以下逻辑对该数组进行排序
return function(a,b){
if(a === null){
return 1;
}
else if(b === null){
return -1;
}
else if(a === b){
return 0;
}
else if(ascending) {
return a < b ? -1 : 1;
}
else if(!ascending) {
return a < b ? 1 : -1;
}
};
我得到以下输出
Ascending : [a, b, d, null,null]
Descending : [d, b, a, null,null]
Expected : [null, null,d, b, a]
我究竟做错了什么?
function getSort (ascending) { // if ascending, `null` will be pushed towards the end of the array by returning 1 var nullPosition = ascending ? 1 : -1 return function (a, b) { // if a is null, push it towards whichever end null elements should end up if (a == null) return nullPosition // Note: at this point, a is non-null (previous if statement handled that case). // // If b is null, it must therefore be placed closer to whichever end the null // elements should end up on. If ascending, null elements are pulled towards // the right end of the array. If descending, null elements are pulled towards // the left. // // Therefore, we return -nullPosition. If ascending, this is -1, meaning a comes // before b; if descending, this is 1, meaning a comes after b. This is // clearly the correct behavior, since ascending will push b, which is null, // towards the end of the array (with -1) and descending will push b towards // the beginning of the array. if (b == null) return -nullPosition // OTHERWISE, both elements are non-null, so sort normally. // if a < b AND // if ascending, a comes first, so return -1 == -nullPosition // if descending, a comes after, so return -nullPosition == -(-1) == 1 if (a < b) return -nullPosition // return the opposite of the previous condition if (a > b) return nullPosition // return 0 if both elements are equal return 0 } } function write (arr) { arr.forEach(function (d) { document.write(d + "<br>")})} var toSort = ['a', 'b', null, 'd', null] var sortA = getSort(true) var sortD = getSort(false) document.write("<br>ASCENDING<br>") write(toSort.sort(sortA)) document.write("<br>DESCENDING<br>") write(toSort.sort(sortD))
您可以使用两次通过方法,首先检查null
值,然后再按字符串排序。
要更改排序顺序,可以交换参数或使用其中一个函数的求和结果。
var data = ['a', 'b', null, 'd', null]; // ascending data.sort(function (a, b) { return (a === null) - (b === null) || ('' + a).localeCompare(b); }); console.log(data); // descending data.sort(function (a, b) { return (b === null) - (a === null) || ('' + b).localeCompare(a); }); console.log(data);
.as-console-wrapper { max-height: 100% !important; top: 0; }
下面的解决方案呢?
var arr = [null, 'e', 'a', 'b', null, 'd', null];
function sortBy(arr, ascending) {
return arr.sort((a, b) => {
if(!a) return ascending ? 1 : -1;
if(!b) return ascending ? -1 : 1;
if (ascending) return a > b ? 1 : -1;
return a > b ? -1 : 1;
})
}
const ascendingArr = sortBy(arr, true);
console.log(ascendingArr);
const decendingArr = sortBy(arr, false);
console.log(decendingArr);
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