How to convert array 2D to 1D in C-CodePudding

I have 2D array arr[i][j]. Where i is the index of list while [j]= list of five elements. For example

arr[0][1,2,3,4,5]  
arr[1][6,7,9,2,1] 
...
arr[n][1,3,2,4,8]

I want to convert it into 1D so that index indicator get remove and have list of elements only. Please guide me.

CodePudding user response：

you can loop through your 2d array and push into a new 1d array

vector<vector<int>> twoD;
vector<int> oneD;
for (int i=0; i<twoD.size(); i  ) {
  for(int j=0; j<twoD[i].size(); j  ) {
    oneD.push_back(twoD[i][j]);
  }
}

return oneD;

CodePudding user response：

a more modern and working solution could be something like this.

std::array<std::array<int,4>,3> ar;
ar[0]={2,3,4,5};
ar[1]={6,7,8,9};
ar[2]={10,11,12,13};

std::vector<int> oneD;
for(const auto& firstLayer : ar){
    for(const auto& secondLayerItem: firstLayer){
       oneD.push_back(secondLayerItem);
    }
}

CodePudding user response：

Consider using a std::span to create a 1D view over the 2D array:

std::span sp(std::data(arr[0]), std::size(arr) * std::size(arr[0]));

Or simpler:

std::span sp(*arr, std::size(arr) * std::size(*arr));

Or if you already have the dimensions of the original array:

std::span sp(*arr, i * j);

Now you can view elements in sp with sp[N]. Demo: https://godbolt.org/z/ebeaEd6xn

Note, span is only a view over the original array, so any modifications on sp's element will be reflected to the original array.