HighFive::ProductSet Class Reference

Selects the Cartesian product of slices. More...

#include <H5Slice_traits.hpp>

Public Member Functions
template<class... Slices>
	ProductSet (const Slices &... slices)

Friends
template<typename Derivate >
class	SliceTraits

Detailed Description

Selects the Cartesian product of slices.

Given a one-dimensional dataset one might want to select the union of multiple, non-overlapping slices. For example,

using Slice = std::array<size_t, 2>;
using Slices = std::vector<Slice>;
auto slices = Slices{{0, 2}, {4, 10}};
dset.select(ProductSet(slices);

to select elements 0, 1 and 4, ..., 9 (inclusive).

For a two-dimensional array one which to select the row specified above, but only columns 2, 3 and 4:

dset.select(ProductSet(slices, Slice{2, 5})); // Analogues with the roles of columns and rows reversed: dset.select(ProductSet(Slice{2, 5}, slices));

One can generalize once more and allow the unions of slices in both x- and y-dimension:

auto yslices = Slices{{1, 5}, {7, 8}};
auto xslices = Slices{{0, 3}, {6, 8}};
dset.select(ProductSet(yslices, xslices));

which selects the following from a 11x8 dataset:

. . . . . . . .
x x x . . . x x
x x x . . . x x
x x x . . . x x
x x x . . . x x
. . . . . . . .
. . . . . . . .
x x x . . . x x
. . . . . . . .
. . . . . . . .
. . . . . . . .

Final twist, the selection along and axis may be discrete indices, from which a vector of, possibly single-element, slices can be constructed. The corresponding types are std::vector<size_t> and size_t for multiple or just a single values. Note, looping over rows or columns one-by-one can be a very serious performance problem. In particular,

// Avoid:
for(auto i : indices) {
    dset.select(i).read<double>();
}

// Use:
std::vector<size_t> tmp(indices.begin(), indices.end());
dset.select(tmp).read<std::vector<double>>();

obvious omit the copy if indices already has the correct type.

The solution works analogous in higher dimensions. A selection sk along axis k can be interpreted as a subset S_k of the natural numbers. The index i is in S_k if it's selected by sk. The ProductSet of s0, ..., sN selects the Cartesian product S_0 x ... x S_N.

Note that the selections along each axis must be sorted and non-overlapping.

Since

3.0

Constructor & Destructor Documentation

ProductSet()

template<class... Slices>

HighFive::ProductSet::ProductSet ( const Slices &...  slices )

inlineexplicit

Friends And Related Symbol Documentation

SliceTraits

template<typename Derivate >

friend class SliceTraits

friend

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The documentation for this class was generated from the following files:

• highfive/bits/H5Slice_traits.hpp
• highfive/bits/H5Slice_traits_misc.hpp