| re: How can i get each coloumn of a 2D array as 1D arrays??
Renjini wrote:[color=blue]
> hi everyone,
> i have a problem. i have been using an FFT method for 1D arrays. now i
> need to extend the code for 2D arrays..i thought it would be simple and
> i managed to implement the FFT method for every row in the array..the
> problem is now that i need to do the same for each of the
> coloumns...and the elements shud not be copied into any other
> arrays..because the FFT is to be applied on the original array...and
> the same must be given as output..can anyone tell me how i could get
> the coloumns each as a 1D array...?? i am including the int main()
> here.
> i'd be so thankful for the help.
>
> int main(int argc, char *argv[])
> {
>
> double x1[][]={{2,3,4,5},{4,-1,2,3},{1,2,3,4}};
> double y1[][]={{-1,0,2,0},{1,2,2,1},{0,0,0,0}};
>
> cout << "\nInput: \n\n";
> for (int i=0;i<3;i++)
> {
> for(int j=0;j<4;j++)
> {
> cout << x1[i][j] << "+" << y1[i][j] <<"i \t";
> }
> cout<<"\n";
> }
>
>
> for(int i=0;i<3;i++)
> {
> // FFT method for each row
>
> FFT(-1,2,x1[i],y1[i]);
> }
>
> /* for (int i=0;i<(sizeof(x1)/sizeof(x1[0]));i++)
> cout << "Output: " << x1[i] << " + i " << y1[i] <<"\n";
>
> //cout << x1[1] <<"\n";*/
> cout<<"\nOuput: \n\n";
> for (int i=0;i<3;i++)
> {
> for(int j=0;j<4;j++)
> {
> cout << x1[i][j] << "+" << y1[i][j] <<"i \t";
> }
> cout<<"\n";
> }
>
> getch();
> return 0;
>
> }
>[/color]
The following class might be useful to you:
//-----------------------------------------------------------------------------
#include <iostream>
template <typename T>
class ColArray {
public:
template <int N, int M>
ColArray(T (&arr)[N][M], int col) : _p(*arr + col), _sz(M) {}
T& operator[](int index) { return *(_p + index * _sz); }
const T& operator[](int index) const { return *(_p + index *
_sz); }
operator T*() { return _p; }
private:
T* _p;
int _sz;
};
int main()
{
int arr[3][3] = {{11, 12, 13},
{21, 22, 23},
{31, 32, 33}};
// Create a new 1D 'array' by passing the original 2D
// array and the column you want (counting from 0).
ColArray<int> col(arr, 2);
for (int i = 0; i < 3; i++)
std::cout << col[i] << std::endl;
return 0;
}
// Output:
// $ ./cols
// 11
// 21
// 31
//-----------------------------------------------------------------------------
I just wrote it now - it automates the task of adding the row size onto
the address of the first element in the column to reach the desired
index in the same column. Unfortunately I there's no way of doing this
more efficiently (that I can see of) given the constraints you
specified. You are going to take a hit calculating either the row or
column FFT because of the way arrays are ordered.
Anyway you should be able to pretend that a ColArray object is normal
array and pass it to your FFT function. If I've missed anything you can
add it to the class yourself - subscripting and array to pointer
decomposition was all I could think of off the top of my head.
To calculate the column FFT:
for (int i = 0; i < 3; i++) {
// FFT method for each row
FFT(-1, 2, ColArray(x1, i), ColArray(y1, i));
}
Hope that helps =)
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