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 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 ele‐
ments 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).
-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
element 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). Elements 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-insensitive 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 dupli‐
cates are determined relative to the comparison used in the
sort. Thus if -index 0 is used, {1 a} and {1 b} would be con‐
sidered 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)
