我有以下for循环,当我使用splice()删除一个项目时,我得到'seconds'是未定义的。我可以检查它是否未定义,但我觉得可能有一种更优雅的方式来做到这一点。他们的愿望是简单地删除一个项目,然后继续前进。
for (i = 0, len = Auction.auctions.length; i < len; i++) {
auction = Auction.auctions[i];
Auction.auctions[i]['seconds'] --;
if (auction.seconds < 0) {
Auction.auctions.splice(i, 1);
}
}
这是这个简单线性时间问题的一个简单线性时间解。
当我运行这个代码片段时,n = 100万,每次调用filterInPlace()需要0.013到0.016秒。一个二次解(例如,公认的答案)将需要它的一百万倍左右。
// Remove from array every item such that !condition(item).
function filterInPlace(array, condition) {
var iOut = 0;
for (var i = 0; i < array.length; i++)
if (condition(array[i]))
array[iOut++] = array[i];
array.length = iOut;
}
// Try it out. A quadratic solution would take a very long time.
var n = 1*1000*1000;
console.log("constructing array...");
var Auction = {auctions: []};
for (var i = 0; i < n; ++i) {
Auction.auctions.push({seconds:1});
Auction.auctions.push({seconds:2});
Auction.auctions.push({seconds:0});
}
console.log("array length should be "+(3*n)+": ", Auction.auctions.length)
filterInPlace(Auction.auctions, function(auction) {return --auction.seconds >= 0; })
console.log("array length should be "+(2*n)+": ", Auction.auctions.length)
filterInPlace(Auction.auctions, function(auction) {return --auction.seconds >= 0; })
console.log("array length should be "+n+": ", Auction.auctions.length)
filterInPlace(Auction.auctions, function(auction) {return --auction.seconds >= 0; })
console.log("array length should be 0: ", Auction.auctions.length)
注意,这只是修改原始数组,而不是创建一个新数组;这样做是有好处的,例如,在数组是程序的单一内存瓶颈的情况下;在这种情况下,您不希望创建另一个相同大小的数组,即使是临时的。
举两个例子:
一个例子
// Remove from Listing the Items Checked in Checkbox for Delete
let temp_products_images = store.state.c_products.products_images
if (temp_products_images != null) {
for (var l = temp_products_images.length; l--;) {
// 'mark' is the checkbox field
if (temp_products_images[l].mark == true) {
store.state.c_products.products_images.splice(l,1); // THIS WORKS
// this.$delete(store.state.c_products.products_images,l); // THIS ALSO WORKS
}
}
}
两个例子
// Remove from Listing the Items Checked in Checkbox for Delete
let temp_products_images = store.state.c_products.products_images
if (temp_products_images != null) {
let l = temp_products_images.length
while (l--)
{
// 'mark' is the checkbox field
if (temp_products_images[l].mark == true) {
store.state.c_products.products_images.splice(l,1); // THIS WORKS
// this.$delete(store.state.c_products.products_images,l); // THIS ALSO WORKS
}
}
}