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