NAME
lsort - Sort the elements of a list
SYNOPSIS
lsort ?options? list
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DESCRIPTION
This command sorts the elements of list, returning a new
list in sorted order. The implementation of the lsort
command uses the merge-sort algorithm which is a stable
sort that has O(n log n) performance characteristics.
By default ASCII sorting is used with the result returned
in increasing order. However, any of the following
options may be specified before list to control the sort
ing process (unique abbreviations are accepted):
-ascii Use string comparison with ASCII col
lation order. This is the default.
-dictionary Use dictionary-style comparison. This
is the same as -ascii except (a) case
is ignored except as a tie-breaker and
(b) if two strings contain embedded
numbers, the numbers compare as inte
gers, not characters. For example, in
-dictionary mode, bigBoy sorts between
bigbang and bigboy, and x10y sorts
between x9y and x11y.
-integer Convert list elements to integers and
use integer comparison.
-real Convert list elements to floating-
point values and use floating compari
son.
-command command Use command as a comparison command.
To compare two elements, evaluate a
Tcl script consisting of command with
the two elements appended as addi
tional arguments. The script should
return an integer less than, equal to,
or greater than zero if the first ele
ment is to be considered less than,
equal to, or greater than the second,
respectively.
-increasing Sort the list in increasing order
(``smallest'' items first). This is
-decreasing Sort the list in decreasing order
(``largest'' items first).
-index index If this option is specified, each of
the elements of list must itself be a
proper Tcl sublist. Instead of sort
ing based on whole sublists, lsort
will extract the index'th element from
each sublist and sort based on the
given element. The keyword end is
allowed for the index to sort on the
last sublist element. For example,
lsort -integer -index 1 {{First 24} {Second 18} {Third 30}}
returns {Second 18} {First 24} {Third
30}. This option is much more effi
cient than using -command to achieve
the same effect.
-unique If this option is specified, then only
the last set of duplicate elements
found in the list will be retained.
Note that duplicates are determined
relative to the comparison used in the
sort. Thus if -index 0 is used, {1 a}
and {1 b} would be considered dupli
cates and only the second element, {1
b}, would be retained.
NOTES
The options to lsort only control what sort of comparison
is used, and do not necessarily constrain what the values
themselves actually are. This distinction is only notice
able when the list to be sorted has fewer than two ele
ments.
The lsort command is reentrant, meaning it is safe to use
as part of the implementation of a command used in the
-command option.
EXAMPLES
Sorting a list using ASCII sorting:
% lsort {a10 B2 b1 a1 a2}
B2 a1 a10 a2 b1
Sorting a list using Dictionary sorting:
% lsort -dictionary {a10 B2 b1 a1 a2}
a1 a2 a10 b1 B2
% lsort -integer {5 3 1 2 11 4}
1 2 3 4 5 11
% lsort -integer {1 2 0x5 7 0 4 -1}
-1 0 1 2 4 0x5 7
Sorting lists of floating-point numbers:
% lsort -real {5 3 1 2 11 4}
1 2 3 4 5 11
% lsort -real {.5 0.07e1 0.4 6e-1}
0.4 .5 6e-1 0.07e1
Sorting using indices:
% # Note the space character before the c
% lsort {{a 5} { c 3} {b 4} {e 1} {d 2}}
{ c 3} {a 5} {b 4} {d 2} {e 1}
% lsort -index 0 {{a 5} { c 3} {b 4} {e 1} {d 2}}
{a 5} {b 4} { c 3} {d 2} {e 1}
% lsort -index 1 {{a 5} { c 3} {b 4} {e 1} {d 2}}
{e 1} {d 2} { c 3} {b 4} {a 5}
Stripping duplicate values using sorting:
% lsort -unique {a b c a b c a b c}
a b c
More complex sorting using a comparison function:
% proc compare {a b} {
set a0 [lindex $a 0]
set b0 [lindex $b 0]
if {$a0 < $b0} {
return -1
} elseif {$a0 > $b0} {
return 1
}
return [string compare [lindex $a 1] [lindex $b 1]]
}
% lsort -command compare \
{{3 apple} {0x2 carrot} {1 dingo} {2 banana}}
{1 dingo} {2 banana} {0x2 carrot} {3 apple}
SEE ALSO
lappend(n), lindex(n), linsert(n), list(n), llength(n),
lrange(n), lreplace(n), lsearch(n)
KEYWORDS
element, list, order, sort
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