lsort

lsort(3tcl)                   Tcl Built-In Commands                  lsort(3tcl)



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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 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.
              Overrides the -nocase option.

       -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).

       -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 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}

       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 ALSO
       list(3tcl), lappend(3tcl), lindex(3tcl), linsert(3tcl), llength(3tcl),
       lsearch(3tcl), lset(3tcl), lrange(3tcl), lreplace(3tcl)

KEYWORDS
       element, list, order, sort



Tcl                                    8.5                           lsort(3tcl)