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     Traversable是所有collections的父类

     Traversable是所有集合层级的最顶端的,他只有一个抽象方法, foreach:

def foreach[U](f: Elem => U)

     实现Traversable只需要定义这个方法,其他方法可以直接继承得到。

foreach 方法以为遍历集合中的所有元素,并且应用传入的方法,f , 对每一个元素。 函数(或者方法,操作)的类型是Elem => U, Elem 是集合元素的类型 而 U是一个任意的结果类型.  函数的f的调用是他的一个副作用,事实上函数的结果都会被 foreach方法丢弃。



  函数分类:Traversable 的方法可以分类如下:

Addition:

         方法名: ++ 

      说明: 同时追加两个traversable,或者追加一个迭代的所有元素到traversable


Map : 

      方法名: map, flatMap, collect

        说明: 通过应用函数到集合的元素中,来产生一个新的集合


Conversions :

      方法名:toArraytoListtoIterabletoSeqtoIndexedSeqtoStreamtoSet,toMap

   说明: 使得 Traversable 变的更加具体。所有这些转换返回的接收器的参数不会改变,如果集合的运行时类型已经匹配了要求的集合类型。 如: 在一个列表中应用 toList,将会调用该列表的 toList方法。


Copying operations :

      方法名 : copyToBuffer,  copyToArray

   说明:作用如他们的名字


Size info:

      方法名:isEmptynonEmptysize, and hasDefiniteSize

   说明:作用如其名,唯一需要说明的是hasDefiniteSize  ,判断一个集合是否有穷还是无穷


Element retrieval: 

      方法名:headlastheadOptionlastOption, and find.

      说明: 头尾方法的定义.  但是有些集合不能很好的定义头尾方法。 如,hash存储是key,value, 又如某些运行时会不断改变元素顺序的。 


Sub-collection retrieval operations :

      方法名: tailinitslicetakedroptakeWhile,dropWhilefilterfilterNotwithFilter

   说明:返回子集合


Subdivision operations : 

      方法名: plitAtspanpartitiongroupBy

   说明:分割集合成几个子集合


Element tests: 

     方法名:existsforallcount

     说明:测试断言(书生:即方法做的事情)是否成立


Folds :

     方法名:foldLeftfoldRight/::\reduceLeftreduceRight

     说明:用二进制的方式操作连续的元素


Specific folds : 

     方法名: sumproductminmax    

     说明:用于特定类型,如数字


String :

    方法名: mkStringaddStringstringPrefix

  说明:转换一个集合到字符串的方式


View:

     方法名: view

   说明:这个方法将单独介绍




Class Traversable中的方法

WHAT IT IS WHAT IT DOES
Abstract Method:
xs foreach f Executes function f for every element of xs.
Addition:
xs ++ ys A collection consisting of the elements of both xs and ys. ys is a TraversableOnce collection, i.e., either a Traversable or an Iterator.
Maps:
xs map f The collection obtained from applying the function f to every element in xs.
xs flatMap f The collection obtained from applying the collection-valued function f to every element in xs and concatenating the results.
xs collect f The collection obtained from applying the partial function f to every element in xs for which it is defined and collecting the results.
Conversions:
xs.toArray Converts the collection to an array.
xs.toList Converts the collection to a list.
xs.toIterable Converts the collection to an iterable.
xs.toSeq Converts the collection to a sequence.
xs.toIndexedSeq Converts the collection to an indexed sequence.
xs.toStream Converts the collection to a lazily computed stream.
xs.toSet Converts the collection to a set.
xs.toMap Converts the collection of key/value pairs to a map. If the collection does not have pairs as elements, calling this operation results in a static type error.
Copying:
xs copyToBuffer buf Copies all elements of the collection to buffer buf.
xs copyToArray(arr, s, n) Copies at most n elements of the collection to array arr starting at index s. The last two arguments are optional.
Size info:
xs.isEmpty Tests whether the collection is empty.
xs.nonEmpty Tests whether the collection contains elements.
xs.size The number of elements in the collection.
xs.hasDefiniteSize True if xs is known to have finite size.
Element Retrieval:
xs.head The first element of the collection (or, some element, if no order is defined).
xs.headOption The first element of xs in an option value, or None if xs is empty.
xs.last The last element of the collection (or, some element, if no order is defined).
xs.lastOption The last element of xs in an option value, or None if xs is empty.
xs find p An option containing the first element in xs that satisfies p, or None if no element qualifies.
Subcollections:
xs.tail The rest of the collection except xs.head.
xs.init The rest of the collection except xs.last.
xs slice (from, to) A collection consisting of elements in some index range of xs (from from up to, and excluding to).
xs take n A collection consisting of the first n elements of xs (or, some arbitrary n elements, if no order is defined).
xs drop n The rest of the collection except xs take n.
xs takeWhile p The longest prefix of elements in the collection that all satisfy p.
xs dropWhile p The collection without the longest prefix of elements that all satisfy p.
xs filter p The collection consisting of those elements of xs that satisfy the predicate p.
xs withFilter p A non-strict filter of this collection. Subsequent calls to map, flatMap, foreach, and withFilter will only apply to those elements of xs for which the condition p is true.
xs filterNot p The collection consisting of those elements of xs that do not satisfy the predicate p.
Subdivisions:
xs splitAt n Split xs at a position, giving the pair of collections (xs take n, xs drop n).
xs span p Split xs according to a predicate, giving the pair of collections (xs takeWhile p, xs.dropWhile p).
xs partition p Split xs into a pair of two collections; one with elements that satisfy the predicate p, the other with elements that do not, giving the pair of collections (xs filter p, xs.filterNot p)
xs groupBy f Partition xs into a map of collections according to a discriminator function f.
Element Conditions:
xs forall p A boolean indicating whether the predicate p holds for all elements of xs.
xs exists p A boolean indicating whether the predicate p holds for some element in xs.
xs count p The number of elements in xs that satisfy the predicate p.
Folds:
(z /: xs)(op) Apply binary operation op between successive elements of xs, going left to right and starting with z.
(xs :\ z)(op) Apply binary operation op between successive elements of xs, going right to left and starting with z.
xs.foldLeft(z)(op) Same as (z /: xs)(op).
xs.foldRight(z)(op) Same as (xs :\ z)(op).
xs reduceLeft op Apply binary operation op between successive elements of non-empty collection xs, going left to right.
xs reduceRight op Apply binary operation op between successive elements of non-empty collection xs, going right to left.
Specific Folds:
xs.sum The sum of the numeric element values of collection xs.
xs.product The product of the numeric element values of collection xs.
xs.min The minimum of the ordered element values of collection xs.
xs.max The maximum of the ordered element values of collection xs.
Strings:
xs addString (b, start, sep, end) Adds a string to StringBuilder b that shows all elements of xs between separators sep enclosed in strings start and end. start, sep, end are all optional.
xs mkString (start, sep, end) Converts the collection to a string that shows all elements of xs between separators sep enclosed in strings start and end. start, sep, end are all optional.
xs.stringPrefix The collection name at the beginning of the string returned from xs.toString.
Views:
xs.view Produces a view over xs.
xs view (from, to) Produces a view that represents the elements in some index range of xs.