Module: Standard C++ Library Library: Numerics
Does not inherit
A numeric array class used to represent a generalized slice from an array
#include <valarray>
namespace std {
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.
namespace std{
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 gslice with starting index, length, and stride as indicated by the arguments.
gslice(const gslice&)
Creates a gslice with starting index, length, and stride as indicated by the slice argument.
size_t start() const;
Returns the starting index of the gslice.
valarray<size_t> size() const;
Returns a valarray<size_t> containing the lengths of the gslice.
valarray<size_t> stride() const;
Returns a valarray<size_t> containing the strides of the gslice.
//
// gslice.cpp
//
#include <valarray.h> // Includes valarray and provides
// stream inserter.
typedef std::valarray<int> valarray_t;
typedef std::valarray<size_t> selector_t;
int main(void) {
// Create a valarray of ints.
valarray_t::value_type ibuf[27] =
{ 0, 1, 2, 3, 4, 5, 6, 7, 8,
9, 10, 11, 12, 13, 14, 15, 16, 17,
18, 19, 20, 21, 22, 23, 24, 25, 26 };
valarray_t vi(ibuf, 27);
// Create length and stride valarray
selector_t::value_type length_buf[3] = {3,3,3};
selector_t::value_type stride_buf[3] = {9,3,1};
selector_t length_val(length_buf, 3);
selector_t stride_val(stride_buf, 3);
// Print out the valarray<int>.
std::cout << "original valarray vi\n\n" << vi << "\n\n";
// Print out all three dimensions (the entire valarray).
std::cout << "vi[gslice(0,{3,3,3},{9,3,1})]\n\n"
<< vi[std::gslice(0,length_val,stride_val)]
<< "\n\n";
// Print a two dimensional slice out of the middle.
selector_t::value_type length_buf2[] = {3, 3};
selector_t::value_type stride_buf2[] = {3, 1};
selector_t length_val2(length_buf2, 2);
selector_t stride_val2(stride_buf2, 2);
std::cout << "vi[gslice(9,{3,3},{3,1})]\n\n"
<< vi[std::gslice(9,length_val2,stride_val2)]
<< "\n\n";
// Print another two dimensional slice out of the middle but
// orthogonal to one we just did.
stride_val2[0] = 9;
stride_val2[1] = 1;
std::cout << "vi[gslice(3,{3,3},{9,1})]\n\n"
<< vi[std::gslice(3,length_val2,stride_val2)]
<< "\n\n";
// Print out the last plane in the middle -- orthogonal to
// both of the previous ones.
stride_val2[0] = 3;
stride_val2[1] = 9;
std::cout << "vi[gslice(1,{3,3},{3,9})]\n\n"
<< vi[std::gslice(1,length_val2,stride_val2)]
<< "\n\n";
// Now how about a diagonal slice, upper left front to lower right
// back.
stride_val2[0] = 3;
stride_val2[1] = 10;
std::cout << "vi[gslice(0,{3,3},{3,10})]\n\n"
<< vi[std::gslice(0,length_val2,stride_val2)]
<< "\n\n";
return 0;
}
Program Output:
original valarray vi
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26]
vi[gslice(0,{3,3,3},{9,3,1})]
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26]
vi[gslice(9,{3,3},{3,1})]
[9,10,11,12,13,14,15,16,17]
vi[gslice(3,{3,3},{9,1})]
[3,4,5,12,13,14,21,22,23]
vi[gslice(1,{3,3},{3,9})]
[1,10,19,4,13,22,7,16,25]
vi[gslice(0,{3,3},{3,10})]
[0,10,20,3,13,23,6,16,26]
valarray, slice_array, slice, gslice_array, mask_array, indirect_array
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 26.3.6
Copyright (c) 1994-2006 Rogue Wave Software, a Quovadx Division.
Licensed under the Apache License, Version 2.0.
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