Elements in one Array (or Collection) But not in another

I apologize again for bringing up perl in context of C# but...

In perl if I have two arrays and want to know what elements are in one but not the other I could do the following (assume @a & @b are already populated):

my %seen // lookup table (hash)
my @aonly //answer

//Build lookup table
@seen{@b} = ();
foreach $item (@a) {
   push (@aonly, $item) unless exists $seen{$item};
}

Another way that might make more sense:

%seen //Lookup table to test membership of B
@aonly //answer

//Build lookup table
foreach $item (@b) {$seen{$item} = 1}

//Find only elements in @a and not in @b
foreach $item (@a) {
   unless ($seen{$item}) {
      //It's not in %seen, so add to @aonly
      push(@aonly,$item);
   }
}

I know the answer must lie with hash tables or dictionaries or the like but can't quite figer it out.

--Richard

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Elements in one Array (or Collection) But not in another

Jameslee20

List<T> ItemsInOneListButNotTheOther<T>(List<T> oneList, List<T> otherList)
{
    List<T> answerList = new List<T>();

    foreach (T value in oneList)
    {
        if (! otherList.Contains(value))
        {
            answerList.Add(value);
        }
    }

    return answerList;
}

SPersels
Hummm. I can't get that code to work. I have two collections, do I need to copy or convert them to a List for this to work
aLaMaT

Just change the signature of the method to take two ICollection objects instead of two Lists.

Mads
Elements in one Array (or Collection) But not in another

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