remove from List using Linq

Question

So, I have a List of objects of class A that contains a List of objects of class B

class A 
{
  ...
  List<B> bs;
}

and I have lists:

List<A> mainList;
List<B> listForRemoval;

How can I, using Linq, "clean" mainList, by removing all objects from bs (for every A in mainList) that exists in listForRemoval?

I hope I didn't confuse you with this question. :)

ExCodeCowboy · Accepted Answer · 2011-06-09 06:08:32Z

4

linq itself is probably not a great fit, but you can use some of it's extension methods. Linq typically is mostly for selection, not processing.

mainList.ForEach(x=>x.bs = x.bs.Where(y=>!listForRemoval.Contains(y)).ToList());

answered Jun 9, 2011 at 6:08

ExCodeCowboy

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2 Comments

VMAtm Over a year ago

This will create many new instances of lists that are overrided.

ExCodeCowboy Over a year ago

@VMAtm - Yeah I would prefer a RemoveAll when dealing with List objects too because you don't know if there are lingering references out there. I was just showing using some of the linq extension methods. I was really just treating as if you were simply dealing with any "IEnumberable".

Heinzi · Accepted Answer · 2011-06-09 10:04:57Z

4

Yes, it's possible, as the other answers have shown. I would, however, choose the following solution which does not use LINQ at all:

foreach (var a in mainList) {
    a.bs.RemoveAll(b => listForRemoval.Contains(b));
}

Advantages:

It's easier to read and understand.
It's not longer than the LINQ-based solutions---in fact, it's shorter than the accepted, LINQ-based answer.
It removes the elements from bs rather than assigning a new list to bs. This might yield better performance and/or be necessary if the list is used in other places as well.

edited Jun 9, 2011 at 10:04

answered Jun 9, 2011 at 6:27

Heinzi

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2 Comments

ExCodeCowboy Over a year ago

I would suggest even when using the "RemoveAll" method there is no reason not to use the the "ForEach" method of the parent List like VMAtm did.

Heinzi Over a year ago

@Xenophile: Personally, I consider foreach (var x in list) ... to be easier to read than list.ForEach(x => ...) (especially if additional levels of nested parenthesis follow), but that might be a matter of taste.

Andrew Cooper · Accepted Answer · 2011-06-09 06:11:06Z

2

foreach (var list in mainList) {
    list.bs = list.bs.Where(b => !listForRemoval.Contains(b)).ToList();
}

edited Jun 9, 2011 at 6:11

answered Jun 9, 2011 at 6:05

Andrew Cooper

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2 Comments

ExCodeCowboy Over a year ago

You need a "!" infront of contains.. you are doing the opposite of what he wanted with the sublist if I read that right.

Andrew Cooper Over a year ago

@Xenophile - Oops. Thanks for the catch. Fixed it now.

VMAtm · Accepted Answer · 2011-06-09 06:19:56Z

2

mainList.ForEach(a => a.bs.RemoveAll(b => listForRemoval.Contains(b)));

answered Jun 9, 2011 at 6:19

VMAtm

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