28 Numerics library [numerics]

28.6 Numeric arrays [numarray]

28.6.2 Class template valarray [template.valarray]

28.6.2.5 Subset operations [valarray.sub]

The member operator[] is overloaded to provide several ways to select sequences of elements from among those controlled by *this.
Each of these operations returns a subset of the array.
The const-qualified versions return this subset as a new valarray object.
The non-const versions return a class template object which has reference semantics to the original array, working in conjunction with various overloads of operator= and other assigning operators to allow selective replacement (slicing) of the controlled sequence.
In each case the selected element(s) shall exist.
valarray operator[](slice slicearr) const;
Returns: A valarray containing those elements of the controlled sequence designated by slicearr.
[Example 1: const valarray<char> v0("abcdefghijklmnop", 16); // v0[slice(2, 5, 3)] returns valarray<char>("cfilo", 5) — end example]
slice_array<T> operator[](slice slicearr);
Returns: An object that holds references to elements of the controlled sequence selected by slicearr.
[Example 2: valarray<char> v0("abcdefghijklmnop", 16); valarray<char> v1("ABCDE", 5); v0[slice(2, 5, 3)] = v1; // v0 == valarray<char>("abAdeBghCjkDmnEp", 16); — end example]
valarray operator[](const gslice& gslicearr) const;
Returns: A valarray containing those elements of the controlled sequence designated by gslicearr.
[Example 3: const valarray<char> v0("abcdefghijklmnop", 16); const size_t lv[] = { 2, 3 }; const size_t dv[] = { 7, 2 }; const valarray<size_t> len(lv, 2), str(dv, 2); // v0[gslice(3, len, str)] returns // valarray<char>("dfhkmo", 6) — end example]
gslice_array<T> operator[](const gslice& gslicearr);
Returns: An object that holds references to elements of the controlled sequence selected by gslicearr.
[Example 4: valarray<char> v0("abcdefghijklmnop", 16); valarray<char> v1("ABCDEF", 6); const size_t lv[] = { 2, 3 }; const size_t dv[] = { 7, 2 }; const valarray<size_t> len(lv, 2), str(dv, 2); v0[gslice(3, len, str)] = v1; // v0 == valarray<char>("abcAeBgCijDlEnFp", 16) — end example]
valarray operator[](const valarray<bool>& boolarr) const;
Returns: A valarray containing those elements of the controlled sequence designated by boolarr.
[Example 5: const valarray<char> v0("abcdefghijklmnop", 16); const bool vb[] = { false, false, true, true, false, true }; // v0[valarray<bool>(vb, 6)] returns // valarray<char>("cdf", 3) — end example]
mask_array<T> operator[](const valarray<bool>& boolarr);
Returns: An object that holds references to elements of the controlled sequence selected by boolarr.
[Example 6: valarray<char> v0("abcdefghijklmnop", 16); valarray<char> v1("ABC", 3); const bool vb[] = { false, false, true, true, false, true }; v0[valarray<bool>(vb, 6)] = v1; // v0 == valarray<char>("abABeCghijklmnop", 16) — end example]
valarray operator[](const valarray<size_t>& indarr) const;
Returns: A valarray containing those elements of the controlled sequence designated by indarr.
[Example 7: const valarray<char> v0("abcdefghijklmnop", 16); const size_t vi[] = { 7, 5, 2, 3, 8 }; // v0[valarray<size_­t>(vi, 5)] returns // valarray<char>("hfcdi", 5) — end example]
indirect_array<T> operator[](const valarray<size_t>& indarr);
Returns: An object that holds references to elements of the controlled sequence selected by indarr.
[Example 8: valarray<char> v0("abcdefghijklmnop", 16); valarray<char> v1("ABCDE", 5); const size_t vi[] = { 7, 5, 2, 3, 8 }; v0[valarray<size_t>(vi, 5)] = v1; // v0 == valarray<char>("abCDeBgAEjklmnop", 16) — end example]