小编Mr.*_*pMe的帖子

我正在尝试在我的mac上设置一个工作环境:

brew install opencv3 --c++11 --with-contrib --with-gphoto2 --with-python3
==> Installing opencv3 from homebrew/homebrew-science

...

==> cmake .. -DCMAKE_C_FLAGS_RELEASE= -DCMAKE_CXX_FLAGS_RELEASE= -DCMAKE_INSTALL
==> make
==> make install
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local.

opencv3 and opencv install many of the same files.

Generally there are no consequences of this for you. If you build your
own software and it requires this formula, you'll need to add to your
build variables:

    LDFLAGS:  -L/usr/local/opt/opencv3/lib
    CPPFLAGS: -I/usr/local/opt/opencv3/include …

我正在比较这两个功能：

double polynomials(const vector<double> & coeffs, double x) {
    double sum = 0.0;
    double factor = 1.0;
    for (double coeff: coeffs) {
        sum += coeff * factor;
        factor *= x;
    }
    return sum;
}

和

double algorithm_polynomials(const vector<double> & coeffs, double x) {
    return reduce(execution::seq, cbegin(coeffs), end(coeffs), 0, [factor=1.0, x](double sum, double coeff) mutable {
        double curr_sum = sum + coeff * factor;
        factor *= x;
        return curr_sum;
    });
}

对于整数系数和整数x，这两个函数的结果相等。但是对于实际价值，结果却有所不同。第一个函数给出的值是正确的，而第二个函数给出的值始终是整数（不一定接近实际答案）。

我的猜测是，每个中间值在求和之前都已转换为整数，但是我不知道为什么会发生这种情况，或者如何解决它。

要运行此代码，请使用

#include <numeric>
#include <vector>
#include <algorithm>
#include …

我有以下代码：（为了勇敢而简化）

public void search(Predicate<String> predicate, Elements elements)
{
    List<SearchResult> searchResults = elements.stream()
        .filter(element -> predicate.test(element.ownText()))
        .map(element -> new SearchResult(element.ownText(), element.baseUri(),element.tagName()))
        .collect(Collectors.toList());
}

但是现在，我想要另一个列表，该列表将包含没有映射的所有过滤元素。是否可以使用流来做到这一点，或者我应该为此更改为 foreach 循环？