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
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 sorting process (unique abbreviations are accepted):
- -ascii
- Use string comparison with Unicode code-point collation
order (the name is for backward-compatibility reasons.) 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 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 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 additional 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 relative to the comparison used in the sort.
Thus if -index 0 is used, {1 a} and {1 b} would be
considered 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¶
list(3tcl), lappend(3tcl), lindex(3tcl), linsert(3tcl), llength(3tcl),
lsearch(3tcl), lset(3tcl), lrange(3tcl), lreplace(3tcl)
KEYWORDS¶
element, list, order, sort
