Remove duplicates from list of object

Question

I have MyObject with field: id, a, b, c, e, f and I have List with 500 000 items, now how can I remove all duplicate items with of the same value of the parameter a, c, f? <

Answer 1

If what you are looking for is speed, and don't mind using up some memory then I would recommend that you use a HashSet, if you are interested in doing some custom comparison, then you can make an IEqualityComparer, something like this:

var original = new ArrayList(); // whatever your original collection is 
var unique = new HasSet(new MyCustomEqualityComparer());

foreach(var item in original)
{
    if(!unique.Contains(item))
        unique.Add(item);
}

return unique;

the issue here is that you may end up gobbling up twice the original memory.

Update:

I made some extra research and I think you can achieve just what you want by simply doing:

var original // your original data
var unique = new HashSet(origin, new CustomEqualityComparer());

that should take care of removing duplicated data as no duplication is allowed in a HashSet. I'd recommend that you also take a look at this question about GetHasCode implementation guidelines.

If you want to know some more about the HashSet class follow these links:

About HashSet
About IEqualityComparer constructor
IEqualityComparer documentation

hope this helps