SS 30Nov2004: The following commands are basic set operations for Tcl lists. They are part of a larger library for functional programming in Tcl that's possible to find at [L1 ]. The proposed commands try to run in O(M+N) time complexity, and to don't mess with the order of the elements when possible.
proc lintersect {a b} {
foreach e $a {
set x($e) {}
}
set result {}
foreach e $b {
if {[info exists x($e)]} {
lappend result $e
}
}
return $result
}
proc lunion {a b} {
foreach e $a {
set x($e) {}
}
foreach e $b {
if {![info exists x($e)]} {
lappend a $e
}
}
return $a
}
proc ldifference {a b} {
foreach e $b {
set x($e) {}
}
set result {}
foreach e $a {
if {![info exists x($e)]} {
lappend result $e
}
}
return $result
}
proc in {list element} {
expr {[lsearch -exact $list $element] != -1}
}MJ - Using 8.5 ni and in, this can be speeded up quite considerable, for instance:
proc ldifference2 {a b} {
set result {}
foreach e $a {
if {$e ni $b} {lappend result $e}
}
return $result
}zashi - The above example using ni doesn't work if $b has more elements than $a.
You can also use lmap to make this more concise. But then to fix the length issue it gets bigger again
proc ldifference3 {list1 list2} {
if {[llength $list1] > [llength $list2]} {
set b $list1
set a $list2
} else {
set a $list1
set b $list2
}
return [lmap e $b {if {$e ni $a} {set e} else continue}]
}