gslice

Valarray helpers

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Interface
• Constructors
• Accessors
• Example
• Warnings
• See Also

A numeric array class used to represent a generalized slice from an array.

Member Functions

size() start() stride()

#include <valarray>
class gslice ;

gslice represents a generalized slice from an array. A generalized slice contains a starting index, a set of lengths and a set of strides. The number of lengths and strides must be equal. Together the lengths and strides allow a slice from a multiple dimension array (with the dimension equal to the number of strides) to be represented on a one dimensional valarray. The gslice maps a set of n indices (ij), where n is equal to the number of strides, to a single index k.

When applied to a valarray using the gslice subscript operator (see valarray) a gslice produces a gslice_array. The gslice_array class creates a view into the original valarray that is tailored to match parameters of the gslice. The elements in a gslice_array are references to the elements in the original array.

class gslice {
public:
  // constructors
  gslice();
  gslice(size_t, const valarray<size_t>&, 
         const valarray<size_t>&);
  gslice (const gslice&);

  // Accessors
  size_t start() const;
  valarray<size_t> size() const;
  valarray<size_t> stride() const;
};

gslice();

Default constructor creates a gslice specifying no elements.

gslice(size_t start, const valarray<size_t>& length,
       const valarray<size_t>& stride);

Creates a slice with starting index, length and stride as indicated by the arguments.

gslice(const gslice&)

Creates a slice with starting index, length and stride as indicated by the slice argument.

size_t start();

Returns the starting index of the gslice.

valarraysize_t> size();

Returns a valarray<size_t> containing the lengths of the gslice.

Valarray<size_t> stride();

Returns a valarray<size_t> containing the strides of the gslice.

//
// gslice.cpp
//
#include "valarray.h" // Contains a valarray stream inserter
 using namespace std;

int main(void)
{
  int ibuf[27] = 
   {0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10};
  size_t len_buf[3] = {3,3,3};
  size_t stride_buf[3] = {9,3,1};

  // create a valarray of ints
  valarray<int>  vi(ibuf,27);

  // create length and stride valarrays
  valarray<size_t> len(len_buf,3);
  valarray<size_t> stride(stride_buf,3);

  // print out the valarray
  cout << vi << endl;

  // Print out all three dimensions (the entire valarray)
  cout << valarray<int>(vi[gslice(0,len,stride)]) << endl;

  // Print a two dimensional slice out of the middle
  valarray<size_t> len2(2);
  len2[0] = 3;
  len2[1] = 3;
  valarray<size_t> stride2(2);
  stride2[0] = 3;
  stride2[1] = 1;
  cout << valarray<int>(vi[gslice(9,len2,stride2)]) << endl;

  // Print another two dimensional slice out of the middle
  // but orthogonal to one we just did
  stride2[0] = 9;
  stride2[1] = 1;
  cout << valarray<int>(vi[gslice(3,len2,stride2)]) << endl;

  // Print out the last plane in the middle,
  // (orthogonal to both of the previous ones)
  stride2[0] = 3;
  stride2[1] = 9;
  cout << valarray<int>(vi[gslice(1,len2,stride2)]) << endl;

  // Now how about a diagonal slice?
  // upper left front to lower right back
  stride2[0] = 3;
  stride2[1] = 10;
  cout << valarray<int>(vi[gslice(0,len2,stride2)]) << endl;
  
  return 0;
}

Program Output

[0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10]
[0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10]
[1,2,3,4,5,6,7,8,9]
[3,4,5,4,5,6,5,6,7]
[1,2,3,4,5,6,7,8,9]
[0,2,4,3,5,7,6,8,10]

If your compiler does not support namespaces, then you do not need the using declaration for std.

valarray, slice_array, slice, gslice_array, mask_array, indirect_array