lsort(n) Tcl Built-In Commands lsort(n)______________________________________________________________________________NAMElsort - Sort the elements of a list
SYNOPSISlsort ?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 Unicode code-point col‐
lation order (the name is for backward-compatibil‐
ity 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 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).
-indices Return a list of indices into list in sorted order
instead of the values themselves.
-index indexList If this option is specified, each of the elements
of list must itself be a proper Tcl sublist (unless
-stride is used). Instead of sorting based on
whole sublists, lsort will extract the indexList'th
element from each sublist (as if the overall ele‐
ment and the indexList were passed to lindex) and
sort based on the given element. For example,
lsort-integer -index 1 \
{{First 24} {Second 18} {Third 30}}
returns {Second 18} {First 24} {Third 30},
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}, and
lsort-index {0 1} {
{{b i g} 12345}
{{d e m o} 34512}
{{c o d e} 54321}
}
returns {{d e m o} 34512} {{b i g} 12345} {{c o d
e} 54321} (because e sorts before i which sorts
before o.) This option is much more efficient than
using -command to achieve the same effect.
-stride strideLength
If this option is specified, the list is treated as
consisting of groups of strideLength elements and
the groups are sorted by either their first element
or, if the -index option is used, by the element
within each group given by the first index passed
to -index (which is then ignored by -index). Ele‐
ments always remain in the same position within
their group.
The list length must be an integer multiple of
strideLength, which in turn must be at least 2.
For example,
lsort-stride 2 {carrot 10 apple 50 banana 25}
returns “apple 50 banana 25 carrot 10”, and
lsort-stride 2 -index 1 -integer {carrot 10 apple 50 banana 25}
returns “carrot 10 banana 25 apple 50”.
-nocase Causes comparisons to be handled in a case-insensi‐
tive manner. Has no effect if combined with the
-dictionary, -integer, or -real options.
-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}
Sorting a dictionary: │
% set d [dict create c d a b h i f g c e] │
c e a b h i f g │
% lsort-stride 2 $d │
a b c e f g h i │
Sorting using striding and multiple indices: │
% # Note the first index value is relative to the group │
% lsort-stride 3 -index {0 1} \ │
{{Bob Smith} 25 Audi {Jane Doe} 40 Ford} │
{{Jane Doe} 40 Ford {Bob Smith} 25 Audi} │
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 ALSOlist(n), lappend(n), lindex(n), linsert(n), llength(n), lsearch(n),
lset(n), lrange(n), lreplace(n)KEYWORDS
element, list, order, sort
Tcl 8.5 lsort(n)
