http://www.purl.org/tcl/home/man/tcl/TclCmd/lindex.htm
lindex list index
Treats its first argument as a Tcl list, returning the index'th element (where index must be an integer if numeric) from it. The index numbers begin with 0 (zero). If the index is negative or greater than or equal to the number of elements in list, an empty string is returned.
If instead of an integer, the string end is provided, the last element of the list is returned. You can use end- integer to offset from the last element.
Also note that recent http://purl.org/tcl/tip/ TIPs 22 and 45 have been implemented and comitted to Tcl 8.4 source CVS tree. Here is a summary of the new functionality from Kevin Kenny:
Jeff Hobbs today committed to the CVS HEAD at Sourceforge the changes described in TIP's 22 (Multiple Index Arguments to lindex), 33 (Add 'lset' Command to Assign to List Elements), and 45 (Empty index lists for [lindex] and lset)
These changes augment the [lindex] command so that it can extract elements from sublists, for example:
[lindex {{a b c} {d e f} {g h i}} 1 1] => eThey also implement an [lset] command that may be used to change individual elements within lists and sublists. Taken together, these commands can be used to treat lists as if they were linear arrays. For instance, the following procedure might be used to reverse the order of elements in a list.
proc reverse { list } {
set i 0
set j [expr { [llength $list] - 1 }]
while { $j > $i } {
set temp [lindex $list $i]
lset list $i [lindex $list $j]
lset list $j $temp
incr i
incr j -1
}
return $list
}Updated documentation for the commands is available in the 'doc/' subdirectory in the source tree. The original proposals may be found at
http://www.purl.org/tcl/tip/22.htm
http://www.purl.org/tcl/tip/33.htm
http://www.purl.org/tcl/tip/45.htm
-- 73 de ke9tv/2, Kevin KENNY GE Corporate R&D, Niskayuna, New York, USA
LES on August 15 2005: What does lindex do that lrange doesn't? pmaage take less time schlenk direct access to elements in nested lists.
proc picknested { argList args } {
Testing:
for {set _depth 0} {$_depth < [llength $args]} {incr _depth} {
set _range [lrange $args $_depth $_depth]
set argList {expand}[lrange $argList $_range $_range]
}
return $argList
}
% picknested {{a b c} {d e {foo bar hey} f} {g h i}} 0
a b cLars H: I'd go further and say lrange still doesn't give you access to
% picknested {{a b c} {d e {foo bar hey} f} {g h i}} 0 1
b
% picknested {{a b c} {d e {foo bar hey} f} {g h i}} 1 2
foo bar hey
% picknested {{a b c} {d e {foo bar hey} f} {g h i}} 1 2 0
foo
% picknested {{a b c} {d e {foo bar hey} f} {g h i}} 1 2 2
heyschlenk Should have said 'easy' access. You can do the same with lrange, yes. You do not need all list commands, most can be replaced by a proc (think lsearch, lsort, lreplace, linsert, lindex). Its just a tradeoff how many list commands exist. (see struct::list for some more). Having more or fewer commands is mostly an optimization in time or space.
Lars H: I'd go further and say lrange still doesn't give you access to the nested elements--it's really {expand} (and in the case of the indices shimmering) that you rely on to pick out elements of lists (undo whatever list-quoting were applied to them). But why bother with lrange, when it's all much simpler with foreach?
proc picknested2 {L args} {
if {$index < 0} then {return {}}
if {$index<0} then {return ""}
foreach L $L {if {[incr index -1]<0} then {break}}
if {$index>=0} then {return ""}
return $L}
}
(Remove first and last if if you don't worry about correct behaviour for out-of-bounds indices.)
See also list, lappend, linsert, llength, lrange, lreplace, lsearch, lsort . Trees as nested lists, lindex forward compatibility
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