Remove specific items from list of objects

Question

I have list of objects:

public class SDesc
{
    public string sensorId { get; set; }
    public string address { get; set; }
}

List<SDesc> desc = new List<SDesc>
{
    new SDesc {sensorId = "1234", address =   "Adams22"},
    new SDesc {sensorId = "5555", address =   "Hourton34"},
    new SDesc {sensorId = "4444", address =   "SaintsRoad55"},
    new SDesc {sensorId = "1258", address =   "BerryAve58"},
    new SDesc {sensorId = "52486", address =   "SaintsRoad2"},
    new SDesc {sensorId = "12361", address =   "TomassonRoad"}
}

And also I have IEnumarable of strings:

IEnumarable<string> sId = {"4444","52486","12361"};

from desc list I need to remove records where sensorsId property exists in sId list.

For example for case above the result I want to get is:

List<SDesc> desc = new List<SDesc>
{
    new SDesc {sensorId = "1234", address =   "Adams22"},
    new SDesc {sensorId = "5555", address =   "Hourton34"},
    new SDesc {sensorId = "1258", address =   "BerryAve58"},
}

Here what I tried:

desc.RemoveAll(obj => obj.sensorId == sId);

But it's not works properly because sID is IEnumarable type.

So my question is how to remove items from desc list where sensorsId property exists in sId list?

Basically the same question as [here](http://stackoverflow.com/q/18895751/993547), and [many other questions here](https://www.google.com/search?q=subtract+list+linq+c%23&oq=subtract+list+linq+c%23#q=subtract+list+linq+c%23+site:stackoverflow.com). — Patrick Hofman, Mar 13 '17 at 08:59

score 3 · Accepted Answer · answered Mar 13 '17 at 08:56

3

You need to use Any with it like:

 desc.RemoveAll(obj => sId.Any(x=> x== obj.sensorId ));

As method name suggests it would check if any of the item in sId matches with the item in desc against sensorId, it will remove those items from List<T>.

answered Mar 13 '17 at 08:56

Ehsan Sajjad

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Thanks for post.What if I desc is type of IEnumarable and not List.what is the way to remove items from it? – Michael Mar 13 '17 at 09:09
in that case you would need to use `Where()` to filter the results and store reference to new `IEnumberable` something like: `var result = desc.Where(obj => sId.Any(x=> x== obj.sensorId ));` – Ehsan Sajjad Mar 13 '17 at 09:11

score 2 · Answer 2 · edited May 23 '17 at 10:30

You can use .Contains() LINQ method to check if a collection contains an item:

desc.RemoveAll(obj => sId.Contains(obj.sensorId));

However, it would lead to multiple enumeration of enumerable sId. It's not a problem in this case since this enumerable is an array in this particular case.

Read more about "possible multiple enumeration":
- Handling warning for possible multiple enumeration of IEnumerable
- Resharper's example code for explaining "Possible multiple enumeration of IEnumerable"

I would recommend converting it to a collection to make sure you enumerate IEnumerable only once.
As suggested by Evk in comments, it is better to use HashSet so that .Contains executes in O(1) time:

List<SDesc> desc = new List<SDesc> {
  new SDesc {sensorId = "1234", address =   "Adams22"},
  new SDesc {sensorId = "5555", address =   "Hourton34"},
  new SDesc {sensorId = "4444", address =   "SaintsRoad55"},
  new SDesc {sensorId = "1258", address =   "BerryAve58"},
  new SDesc {sensorId = "52486", address =   "SaintsRoad2"},
  new SDesc {sensorId = "12361", address =   "TomassonRoad"}
};

IEnumarable<string> sId = {"4444","52486","12361"};
var sIdsSet = new HashSet(sId);

desc.RemoveAll(obj => sIdsSet.Contains(obj.sensorId));

If convert it to anything, I'd say it should be `HashSet` and not array. — Evk, Mar 13 '17 at 09:01
@Yeldar Kurmangaliyev: shouldn't you remove negator (!) from your line: `desc.RemoveAll(x => !sIdsArray.Contains(x.sensorId));` Michael needs everything that's not in sId List — tretom, Mar 13 '17 at 09:03
@Evk Thank you! I missed that performance improvement possibility :) Just have updated my answer. — Yeldar Kurmangaliyev, Mar 13 '17 at 09:04

Remove specific items from list of objects

2 Answers2