您好我正在尝试通过其ID在localStorage中对某些数据进行排序。
数据格式如下: {“Brand”:“Acura”,“Model”:“选择你的模特”,“年龄”:“1998”,“KM”:“10”,“姓名”:“Harry”,“ContactInfo”:“123456677” }
我希望按KM值的最低到最高顺序进行排序。
我的本地存储密钥是注册的,这是我正在使用的代码:
function Qsort() {
var mymain = JSON.parse(localStorage.getItem("register"));
var result = quicksort(mymain, 0, mymain.length - 1);
// the following line fo code shows the final result of the sorted numbers or strings
console.log(mymain);
console.log(quicksort(mymain, 0, mymain.length - 1));
return result;
}
function quicksort(mymain, left, right) {
var index;
// checks if there are more than one numbers
if (mymain.length > 1) {
// partition will find a pivot then split leist in two either left of right.
// Left list contains everything that is smaller than the pivot and the right contians everythign larger than pivot
index = partition(mymain, left, right);
// will treat left side aas a new problem and will then run the sort
if (left < index - 1){
quicksort(mymain, left, index - 1)
}
// will treat right side as a new problem and will then run the sort
if (index < right) {
quicksort(mymain, index, right)
}
}
return mymain
}
// Divides the whole function
function partition(mymain, left, right) {
var pivot = mymain[Math.floor((right + left) / 2)],
i = left,
j = right;
while (i <= j) {
while (mymain[i] < pivot) {
i++;
}
while (mymain[j] > pivot) {
j--;
}
if (i <= j) {
swap(mymain, i, j);
i++;
j--;
}
}
return i;
}
// swaps the values based on how high or low the number is
function swap(mymain, firstIndex, secondIndex) {
var temp = mymain[firstIndex];
mymain[firstIndex] = mymain[secondIndex];
mymain[secondIndex] = temp;
}
我应该如何处理var mymain
部分,以便它只获取KM下定义的值。
答案 0 :(得分:0)
假设"register"
中localStorage
的项目是一个数组,你可以简单地做...
var mymain = JSON.parse(localStorage.getItem("register"))
var justKMs = mymain.map(function(data){ return data.KM; });
但是这会返回一个只包含KM值的数组,因此您最终必须搜索mymain
列表以获取其余数据,我认为这不是您想要的。< / p>
另一种方法是添加&#34;查找&#34;告诉quicksort的功能&#34;如何&#34;获取要用于排序的值。我们将查找函数签名定义为function lookup( item ) => value
,其中item
是当前正在排序的列表中的内容,value
是要排序的值。
以下是来自computer-science-in-javascript的快速排序版本,其中添加了&#34;查找&#34;功能
// the swap function doesn't need to change
function swap(items, firstIndex, secondIndex) {
var temp = items[firstIndex];
items[firstIndex] = items[secondIndex];
items[secondIndex] = temp;
}
// you will need to pass the lookup function into partition
function partition(items, left, right, lookup) {
// here you need to use "lookup" to get the proper pivot value
var pivot = lookup(items[Math.floor((right + left) / 2)]),
i = left,
j = right;
while (i <= j) {
// here is where you will do a lookup instead of just "items[i]"
while (lookup(items[i]) < pivot) {
i++;
}
// also use lookup here
while (lookup(items[j]) > pivot) {
j--;
}
if (i <= j) {
swap(items, i, j);
i++;
j--;
}
}
return i;
}
function quickSort(items, left, right, lookup) {
var index;
// performance - don't sort an array with zero or one items
if (items.length > 1) {
// fix left and right values - might not be provided
left = typeof left != "number" ? 0 : left;
right = typeof right != "number" ? items.length - 1 : right;
// set a default lookup function just in case
if (typeof lookup !== 'function') {
// the default lookup function just returns the item passed in
lookup = function (item) {
return item;
};
}
index = partition(items, left, right, lookup);
if (left < index - 1) {
quickSort(items, left, index - 1, lookup);
}
if (index < right) {
quickSort(items, index, right, lookup);
}
}
return items;
}
然后&#34;查找&#34;数据集的函数将是......
function kmLookup( data ) {
return data.KM;
}
......高阶函数的力量
作为旁注,如果你真的没有和quicksort结婚,你可以选择懒人选项(或者根据你的观点选择智能选项)并在Array原型上使用sort
方法...
var mymain = JSON.parse(localStorage.getItem("register"));
// the sort function sorts the array in place,
// so after this next line mymain will be sorted
mymain.sort(function (a, b) {
return a.KM - b.KM;
});
假设您没有使用非常大的数据集,这可能是最好的解决方案。 MDN Array.prototype.sort() docs