实战Tcl和TK程序设计 §5 Tcl列表

 

§5    Tcl列表

本章涉及的命令有: list, lindex, llength, lrange, lappend, linsert, lreplace, lsearch, lset, lsort, concat, join, and split.

       列表与命令拒用相同的结构,最好是吧列表当作一种操作而不是语法.foreach在列表中广泛使用.eval也很相关.

 

大列表的性能一般都比较差,建议使用数组.列表不适合处理非结构化的数据.

Tcl列表

一系列值,用空格分隔,是具有特殊解释的字符串.

Table 5-1. List-related commands
list arg1 arg2 ...	Creates a list out of all its arguments.
lindex list ?i ...?	Returns the ith element from list. Specifying multiple index elements allows you to descend into nested lists easily.
llength list	Returns the number of elements in list.
lrange list i j	Returns the ith through jth elements from list.
lappend listVar arg ...	Appends elements to the value of listVar.
linsert list index arg arg ...	Inserts elements into list before the element at position index. Returns a new list.
lreplace list i j arg arg ...	Replaces elements i through j of list with the args. Returns a new list.
lsearch ?options? list value	Returns the index of the element in list that matches the value according to the options. Glob matching is the default. Returns -1 if not found.
lset listVar ?i ...? newValue	Set the ith element in variable listVar to newValue. (Tcl 8.4)
lsort ?switches? list	Sorts elements of the list according to the switches: -ascii, -dictionary, -integer, -real, -increasing, -decreasing, -index ix, -unique, -command command. Returns a new list.
concat list list ...	Joins multiple lists together into one list.
join list joinString	Merges the elements of a list together by separating them with joinString.
split string splitChars	Splits a string up into list elements, using the characters in splitChars as boundaries between list elements.

 

构建列表:

实例1：用list命令创建列表：

% set x {1 2}
1 2
% set y \$foo
$foo
% set l1 [list $x "a b" $y]
{1 2} {a b} {$foo}
% set l2 [list $l1 $x]
{{1 2} {a b} {$foo}} {1 2}
%

 

实例2：用lappend 命令添加元素到列表：

% lappend new 1 2
1 2
% lappend new 3 "4 5"
1 2 3 {4 5}
%

实例3：用lset 设置元素的值：
可以设置list 的元素，也可以把list的一个元素再当作一个list。
% lset new "a b c"
a b c
% lset new 1 "d e"
a {d e} c
% lset new 1 0 "g h"
a {{g h} e} c
%

 

实例4：用contact 连接list
% set x {4 5 6}
4 5 6
% set y {2 3}
2 3
% set z 1
1
% concat $z $y $x
1 2 3 4 5 6
%

实例5：用contact 和list比较

% set x {1 2}

1 2

% set y "$x 3"

1 2 3

% set y [concat $x 3]

1 2 3

% set s { 2 }

 2

% set y "1 $s 3"

1  2  3

% set y [concat 1 $s 3]

1 2 3

% set z [list $x $s 3]

{1 2} { 2 } 3

可见contact会消除一层列表结构.

 

获取列表元素

% llength { a b  {c d} "e f g" h}

5

% set x {1 2 3}

1 2 3

% lindex $x 1  

2

列表的索引从零开始计数

 

% set x {1 2 3 4 5 }

1 2 3 4 5

% lindex $x end-1

4

% lindex $x end

5

% lrange $x 2 end 

3 4 5

%

 

修改列表

% set x {1 2 3 4 5 }

1 2 3 4 5

% linsert $x 3 30

1 2 3 30 4 5

% set x

1 2 3 4 5

% linsert $x -30 30     

30 1 2 3 4 5

% linsert $x 30 30

1 2 3 4 5 30

%

 

 

实例6：用lreplace修改list

 

% set x [list a {b c} e d]

a {b c} e d

% lreplace $x 1 2 B C

a B C d

% set x

a {b c} e d

% lreplace $x 0 0

{b c} e d

%

可见原list并没有修改.

 

修改列表

 

% lsearch {here is a list} l*

3

实例7：根据值来删除列表元素

 

#

# Example 5-7

# Deleting a list element by value.

#

 

proc ldelete { list value } {

       set ix [lsearch -exact $list $value]

       if {$ix >= 0} {

              return [lreplace $list $ix $ix]

       } else {

              return $list

       }

}

 

对列表进行排序

排序不修改原值,排序的类型有:

-ascii, -dictionary, -integer, or –real

升序和降序-increasing or -decreasing

 

% lsort -ascii {a Z n2 n100}

Z a n100 n2

%

% lsort -dictionary {a Z n2 n100}

a n2 n100 Z

%

%

实例7: 根据last name 排序:

 

% proc NameCompare {a b} {

   set alast [lindex $a end]

   set blast [lindex $b end]

   set res [string compare $alast $blast]

   if {$res != 0} {

      return $res

   } else {

      return [string compare $a $b]

   }

}

% set list {{Brent B. Welch} {John Ousterhout} {Miles Davis}}

{Brent B. Welch} {John Ousterhout} {Miles Davis}

% lsort -command NameCompare $list

{Miles Davis} {John Ousterhout} {Brent B. Welch}

Split 命令

% set line {welch:*:28405:100:Brent Welch:/usr/welch:/bin/csh}

welch:*:28405:100:Brent Welch:/usr/welch:/bin/csh

% split $line :

welch * 28405 100 {Brent Welch} /usr/welch /bin/csh

 

 

join命令

% join {1 {2 3} {4 5 6}} :

1:2 3:4 5 6

%