cppdraft_translate/cppdraft/valarray/sub.md

[valarray.sub]

29 Numerics library [numerics]

29.6 Numeric arrays [numarray]

29.6.2 Class template valarray [template.valarray]

29.6.2.5 Subset operations [valarray.sub]

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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.

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valarray operator[](slice slicearr) const;

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Returns: A valarray containing those elements of the controlled sequence designated by slicearr.

[Example 1: const valarray v0("abcdefghijklmnop", 16);// v0[slice(2, 5, 3)] returns valarray("cfilo", 5) — end example]

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slice_array<T> operator[](slice slicearr);

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Returns: An object that holds references to elements of the controlled sequence selected by slicearr.

[Example 2: valarray v0("abcdefghijklmnop", 16); valarray v1("ABCDE", 5); v0[slice(2, 5, 3)] = v1;// v0 == valarray("abAdeBghCjkDmnEp", 16); — end example]

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valarray operator[](const gslice& gslicearr) const;

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Returns: A valarray containing those elements of the controlled sequence designated by gslicearr.

[Example 3: const valarray 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("dfhkmo", 6) — end example]

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gslice_array<T> operator[](const gslice& gslicearr);

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Returns: An object that holds references to elements of the controlled sequence selected by gslicearr.

[Example 4: valarray v0("abcdefghijklmnop", 16); valarray 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("abcAeBgCijDlEnFp", 16) — end example]

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valarray operator[](const valarray<bool>& boolarr) const;

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Returns: A valarray containing those elements of the controlled sequence designated by boolarr.

[Example 5: const valarray v0("abcdefghijklmnop", 16);const bool vb[] = { false, false, true, true, false, true };// v0[valarray(vb, 6)] returns// valarray("cdf", 3) — end example]

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mask_array<T> operator[](const valarray<bool>& boolarr);

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Returns: An object that holds references to elements of the controlled sequence selected by boolarr.

[Example 6: valarray v0("abcdefghijklmnop", 16); valarray v1("ABC", 3);const bool vb[] = { false, false, true, true, false, true }; v0[valarray(vb, 6)] = v1;// v0 == valarray("abABeCghijklmnop", 16) — end example]

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valarray operator[](const valarray<size_t>& indarr) const;

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Returns: A valarray containing those elements of the controlled sequence designated by indarr.

[Example 7: const valarray v0("abcdefghijklmnop", 16);const size_t vi[] = { 7, 5, 2, 3, 8 };// v0[valarray<size_t>(vi, 5)] returns// valarray("hfcdi", 5) — end example]

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indirect_array<T> operator[](const valarray<size_t>& indarr);

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Returns: An object that holds references to elements of the controlled sequence selected by indarr.

[Example 8: valarray v0("abcdefghijklmnop", 16); valarray v1("ABCDE", 5);const size_t vi[] = { 7, 5, 2, 3, 8 }; v0[valarray<size_t>(vi, 5)] = v1;// v0 == valarray("abCDeBgAEjklmnop", 16) — end example]