lsort
lsort(n) Tcl Built-In Commands lsort(n)
______________________________________________________________________________
NAME
lsort - Sort the elements of a list
SYNOPSIS
lsort ?options? list
_________________________________________________________________
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 char-
acteristics.
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 sorting process (unique abbreviations are
accepted):
-ascii Use string comparison with ASCII collation 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 integers, not char-
acters. 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 comparison.
-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 element 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 the default.
-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 sorting 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, and end-index sorts on a sublist |
element offset from the end. For example,
lsort -integer -index 1 {{First 24} {Second 18} {Third 30}}
returns {Second 18} {First 24} {Third 30}, and |
lsort -index end-1 {{a 1 e i} {b 2 3 f g} {c 4 5 6 d h}}|
returns {c 4 5 6 d h} {a 1 e i} {b 2 3 f g}. This
option is much more efficient 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 rel-
ative to the comparison used in the sort. Thus if
-index 0 is used, {1 a} and {1 b} would be consid-
ered duplicates 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 noticeable when the list to be sorted has
fewer than two elements.
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
Sorting lists of integers:
% 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), lre-
place(n), lsearch(n)
KEYWORDS
element, list, order, sort
Tcl 8.3 lsort(n)
