我尝试在Playground中使用以下代码将二维数组转换为一维数组后添加：
let twoDimensionalArray = [[1, 3, 5], [2, 4, 6], [12, 15, 16]]
let oneDimensionalArray = twoDimensionalArray.flatMap { $0.map { $0 += 2 } }
print(oneDimensionalArray)
但是我收到错误：
变异运算符的左侧不可更改：'$ 0'是不变的
我还发现Apple Documentation中不推荐使用flatmap方法，所以我应该做些什么？
答案 0 :(得分：1)
您几乎是正确的。您只需要删除=：
let twoDimensionalArray = [[1, 3, 5], [2, 4, 6], [12, 15, 16]]
let oneDimensionalArray = twoDimensionalArray.flatMap { $0.map { $0 + 2 } }
print(oneDimensionalArray) // [3, 5, 7, 4, 6, 8, 14, 17, 18]
您可以通过对值（$0）进行操作和其他操作来对更改（$0 += 2）进行更改，而不是直接更改（即#include <Eigen/Eigen>
#include <iostream>
using namespace Eigen;
template <typename Derived>
auto f(DenseBase<Derived>& x) {
auto max_x = x.colwise().maxCoeff().eval();
x = x.rowwise() + max_x;
return max_x;
}
int main() {
Array<float, 3, 3> M1, M2;
M1 << 1, 2, 3,
4, 5, 6,
7, 8, 9;
M2 = M1;
std::cout << M1 << "\n";
std::cout << "no transpose\n";
Array<float, 3, 1> max_x = f(M1);
std::cout << M1 << "\n";
std::cout << max_x << "\n";
std::cout << "transpose\n";
auto m2_t = M2.transpose();
Array<float, 1, 3> max_x2 = f(m2_t);
std::cout << M2 << "\n";
std::cout << max_x2 << "\n";
}
）。