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cppdraft/valarray/sub.md

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+[valarray.sub]
+
+# 29 Numerics library [[numerics]](./#numerics)
+
+## 29.6 Numeric arrays [[numarray]](numarray#valarray.sub)
+
+### 29.6.2 Class template valarray [[template.valarray]](template.valarray#valarray.sub)
+
+#### 29.6.2.5 Subset operations [valarray.sub]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7624)
+
+The member operator[] is overloaded to provide several ways to select
+sequences of elements from among those controlled by *this[.](#1.sentence-1)
+
+Each of these
+operations returns a subset of the array[.](#1.sentence-2)
+
+The const-qualified versions return this
+subset as a new valarray object[.](#1.sentence-3)
+
+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[.](#1.sentence-4)
+
+In each case the selected element(s) shall exist[.](#1.sentence-5)
+
+[🔗](#lib:operator%5b%5d,valarray_)
+
+`valarray operator[](slice slicearr) const;
+`
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7640)
+
+*Returns*: A valarray containing those
+elements of the controlled sequence designated by slicearr[.](#2.sentence-1)
+
+[*Example [1](#example-1)*: const valarray<char> v0("abcdefghijklmnop", 16);// v0[slice(2, 5, 3)] returns valarray<char>("cfilo", 5) — *end example*]
+
+[🔗](#lib:operator%5b%5d,valarray__)
+
+`slice_array<T> operator[](slice slicearr);
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7658)
+
+*Returns*: An object that holds references to elements of the controlled
+sequence selected by slicearr[.](#3.sentence-1)
+
+[*Example [2](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray___)
+
+`valarray operator[](const gslice& gslicearr) const;
+`
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7678)
+
+*Returns*: A valarray containing those
+elements of the controlled sequence designated by gslicearr[.](#4.sentence-1)
+
+[*Example [3](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray____)
+
+`gslice_array<T> operator[](const gslice& gslicearr);
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7700)
+
+*Returns*: An object that holds references to elements of the controlled
+sequence selected by gslicearr[.](#5.sentence-1)
+
+[*Example [4](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray_____)
+
+`valarray operator[](const valarray<bool>& boolarr) const;
+`
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7723)
+
+*Returns*: A valarray containing those
+elements of the controlled sequence designated by boolarr[.](#6.sentence-1)
+
+[*Example [5](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray______)
+
+`mask_array<T> operator[](const valarray<bool>& boolarr);
+`
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7743)
+
+*Returns*: An object that holds references to elements of the controlled
+sequence selected by boolarr[.](#7.sentence-1)
+
+[*Example [6](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray_______)
+
+`valarray operator[](const valarray<size_t>& indarr) const;
+`
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7764)
+
+*Returns*: A valarray containing those
+elements of the controlled sequence designated by indarr[.](#8.sentence-1)
+
+[*Example [7](#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*]
+
+[🔗](#lib:operator%5b%5d,valarray________)
+
+`indirect_array<T> operator[](const valarray<size_t>& indarr);
+`
+
+[9](#9)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7784)
+
+*Returns*: An object that holds references to elements of the controlled
+sequence selected by indarr[.](#9.sentence-1)
+
+[*Example [8](#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*]