保留std :: vector的前N个元素。并删除其余的 [英] Keeping the first N elements of a std::vector<> and removing the rest

问题描述

我的 C ++ 应用程序中有一个 std :: vector< int> 变量。向量的大小在运行时确定，但通常约为 1000 。

I have a std::vector<int> variable in my C++ application. The size of the vector is determined at runtime, but is typically about 1000.

我已经对此向量进行了排序（效果很好），排序之后，我只想保留前一个 50 元素。

I have sorted this vector (which works well), and after sorting, I would like to keep only the first 50 elements.

我尝试过：

kpts.erase(kpts.begin() + 50, kpts.end());

其中 kpts 是我的向量，表现太恐怖了！大概是因为擦除的操作方式。

where kpts is my vector, and the performance is horrible! Presumably because of the way erase operates.

有没有办法只保留向量的前 50 个元素？似乎应该很明显，但是我找不到解决办法。

Is there a way to only keep the first 50 elements of a vector? It seems like it should be obvious, but I can't find a way to do this.

推荐答案

是的，您可以使用 std :: vector :: resize ，如果向量的长度大于n，则会截断。

Yes, you can use std::vector::resize, which just truncates if the length of the vector is greater than n.

参见此处： http://www.cplusplus.com/reference/vector/vector/resize /

std::vector<int> myvector;

for (int i=1;i<1000;i++) myvector.push_back(i);

myvector.resize(50);
// myvector will contain values 1..50

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