[WJG] (16/Feb/06) A simple proc to compare the contents of two lists. It returns a list equal to the differences.

 #----------------
 # compare list a with b
 #----------------
 proc listcomp {a b} {
  foreach i $a {
    if {[lsearch -exact $b $i]==-1} {
      lappend diff $i
    }
  }
  return $diff
 }

 catch {console show}
 set a {1 2 3 4 5 6}
 set b {2 4 6 8}

 puts "list a = \{$a\}\nlist b = \{$b\}\nThe difference between a and b is \{[listcomp $a $b]\}."

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[male] - 2006-02-16: reading the title I thought about something like "'''string compare'''".

So what's about this approach of a kind of list compare '''lcompare''':

 proc lcompare {list1 list2} {
     set length1 [llength $list1];
     set length2 [llength $list2];

     if {$length1 < $length2} {
         return [expr {double(-1)}];
     } elseif {$length1 > $length2} {
         return [expr {double(1)}];
     }

     if {[lindex $list1 0] eq $list1} {
         return [expr {double([string compare $list1 $list2])}];
     }

     set result [expr {double(0)}];

     foreach element1 $list1 element2 $list2 {
         set result [expr {$result + [lcompare $element1 $element2]}];
     }

     return [expr {$result / $length1}];
 }

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