[CJB]:  Returns the list without duplicate elements.  This is different from [[[lsort] -unique]] in that it maintains the list ordering.  It also keeps the first element encountered and removes subsequent callings.

======
proc uniqueList {list} {
  set new {}
  foreach item $list {
    if {[lsearch $new $item] < 0} {
      lappend new $item
    }
  }
  return $new
}
======

[AMG]: Here's another way which internally uses a hash table (amortized constant time per element, linear time overall) instead of a linear search (linear time per element, quadratic time overall):

======
proc uniqueList2 {list} {
  set dict {}
  foreach item $list {
    dict set dict $item ""
  }
  dict keys $dict
}
======

Performance timing:

======
set test [split "this is my test data" ""]
llength $test                                    ;#    20 elements
time {uniqueList  $test} 100000                  ;#    20.78 microseconds per iteration
time {uniqueList2 $test} 100000                  ;#    13.6  microseconds per iteration
set test [lrepeat 1000 {*}$test]; list
llength $test                                    ;# 20000 elements
time {uniqueList  $test} 1000                    ;# 17562.0 microseconds per iteration
time {uniqueList2 $test} 1000                    ;#  6844.0 microseconds per iteration
======

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