Seq trait 代表sequences. 一个序列继承自iterable,，有一个length方法，并且他的元素有固定的索引位置，位置从0开始。
在sequences上操作，如下表，分为几种：
Indexing and length
方法：
apply,isDefinedAt,length,indices, andlengthCompare
apply方法用于建立索引，因此类型Seq[T]的一个序列是一个partial函数，他获取一个int参数，并且产生了一个类型T的序列。综上，Seq[T]扩展了 PartialFunction[Int, T]。
允许比较两个sequences序列的长度，甚至有一个可以是无限大lengthCompare
Index search operations
方法：
indexOf,lastIndexOf,indexOfSlice,lastIndexOfSlice,indexWhere,lastIndexWhere,segmentLength,prefixLength返回索引或者匹配一些断言
Addition operations
方法：
+:,:+,padTo返回一些新的序列，通过头尾增加元素
Update operations
方法：
updated,patch返回一个新的序列，通过更新
Sorting operations
方法：
sorted,sortWith,sortBy,排序，根据多个标准
reversal operations
方法：
reverse,reverseIterator,reverseMap倒序产生或者处理一个序列
Comparisons
方法：
startsWith,endsWith,contains,containsSlice,corresponds比较连个元素或者在一个序列中查找一个元素
Multiset
方法：
intersect,diff,union,distinct在两个序列的元素上做类set的操作，或者移除重复值（这个估计是指单序列中）
如果一个序列是可变的（mutable）,会提供一个额外的方法，update(书生：区别updated)，它能让序列的元素更新。正如在Scala中，语法如seq(idx)=elem 仅仅是seq.update(idx,elem)的一个简写，可以说update给予了一些语法上的便利。
updates: 返回一个被修改后的新的序列代替原序列,对所有序列有效。
update: 修改序列中的元素， 只对可变mutable序列有效
Class Seq 函数
序列
| WHAT IT IS | WHAT IT DOES |
|---|---|
| Indexing and Length: | |
xs(i) |
(or, written out, xs apply i). The element of xs at index i. |
xs isDefinedAt i |
Tests whether i is contained in xs.indices. |
xs.length |
The length of the sequence (same as size). |
xs.lengthCompare ys |
Returns -1 if xs is shorter than ys, +1 if it is longer, and 0 is they have the same length. Works even if one if the sequences is infinite. |
xs.indices |
The index range of xs, extending from 0 to xs.length - 1. |
| Index Search: | |
xs indexOf x |
The index of the first element in xs equal to x (several variants exist). |
xs lastIndexOf x |
The index of the last element in xs equal to x (several variants exist). |
xs indexOfSlice ys |
The first index of xs such that successive elements starting from that index form the sequence ys. |
xs lastIndexOfSlice ys |
The last index of xs such that successive elements starting from that index form the sequence ys. |
xs indexWhere p |
The index of the first element in xs that satisfies p (several variants exist). |
xs segmentLength (p, i) |
The length of the longest uninterrupted segment of elements in xs, starting with xs(i), that all satisfy the predicate p. |
xs prefixLength p |
The length of the longest prefix of elements in xs that all satisfy the predicate p. |
| Additions: | |
x +: xs |
A new sequence that consists of x prepended to xs. |
xs :+ x |
A new sequence that consists of x appended to xs. |
xs padTo (len, x) |
The sequence resulting from appending the value x to xs until length len is reached. |
| Updates: | |
xs patch (i, ys, r) |
The sequence resulting from replacing r elements of xs starting with i by the patch ys. |
xs updated (i, x) |
A copy of xs with the element at index i replaced by x. |
xs(i) = x |
(or, written out, xs.update(i, x), only available for mutable.Seqs). Changes the element of xs at index i to x. |
| Sorting: | |
xs.sorted |
A new sequence obtained by sorting the elements of xs using the standard ordering of the element type of xs. |
xs sortWith lt |
A new sequence obtained by sorting the elements of xs using lt as comparison operation. |
xs sortBy f |
A new sequence obtained by sorting the elements of xs. Comparison between two elements proceeds by mapping the function f over both and comparing the results. |
| Reversals: | |
xs.reverse |
A sequence with the elements of xs in reverse order. |
xs.reverseIterator |
An iterator yielding all the elements of xs in reverse order. |
xs reverseMap f |
A sequence obtained by mapping f over the elements of xs in reverse order. |
| Comparisons: | |
xs startsWith ys |
Tests whether xs starts with sequence ys (several variants exist). |
xs endsWith ys |
Tests whether xs ends with sequence ys (several variants exist). |
xs contains x |
Tests whether xs has an element equal to x. |
xs containsSlice ys |
Tests whether xs has a contiguous subsequence equal to ys. |
(xs corresponds ys)(p) |
Tests whether corresponding elements of xs and ys satisfy the binary predicate p. |
| Multiset Operations: | |
xs intersect ys |
The multi-set intersection of sequences xs and ys that preserves the order of elements in xs. |
xs diff ys |
The multi-set difference of sequences xs and ys that preserves the order of elements in xs. |
xs union ys |
Multiset union; same as xs ++ ys. |
xs.distinct |
A subsequence of xs that contains no duplicated element. |
scala.collection.immutable.List
and
scala.collection.immutable.Stream
，频繁调用indexed序列的
scala.Array
and
scala.collection.mutable.ArrayBuffer
.
Vector提供了一个令人感兴趣的折中，在indexed和linear,他能有效的确保稳定的index和linear访问的时间总开销 。 因此，他是一个非常好的混合访问模式。
