Filtering Linq based on Enum, with a specific unique value exception

Question

In order to simplify, let say I have MyEnum and MyClass:

enum MyEnum
{
    Undefined = 0,
    A = 1,
    B = 2,
    C = 3,
    D = 4
}

class MyClass { MyEnum MyEnumValue { get; set; } }

In order to filter a list of MyClass by a MyEnum value I'm using:

list.Where(r => r.MyEnumValue == myEnum);

But if the MyEnum is equal to specific value (lets say MyEnum.B) I would need the list to return also any values that equal to MyEnum.B or MyEnum.A.

This is what I've came up with:

public static MyClass MyClass_By_MyEnum(IEnumarable<MyClass> list, MyEnum myEnum)
{
    if (myEnum == MyEnum.B)
    {
        return list.Where(r =>
                        r.MyEnumValue == MyEnum.A || 
                        r.MyEnumValue == MyEnum.B ||
                        r.MyEnumValue == MyEnum.C
                    ).FirstOrDefault();
    }
    else
    {
        return list.Where(r => r.MyEnumValue == myEnum).FirstOrDefault();
    }
}

Is there any way achieving this using one line only? without the if else statement?

EDIT 1: I'm searching for a better design based solution, any suggestion?

could you not just cast to int and use a >= or <= operator? — jazb
– jazb, Commented May 15, 2019 at 5:29

John Wu · Accepted Answer · 2019-05-15 05:38:07Z

4

Use an array. Also, you don't need to use Where since you can pass the delegate to FirstOrDefault.

var lookFor = new [] { MyEnum.A, MyEnum.B, MyEnum.C };
return list.FirstOrDefault(r => lookFor.Contains(r.MyEnumValue));

answered May 15, 2019 at 5:38

John Wu

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1 Comment

Prasad Telkikar Over a year ago

why not !=, it will reduce linq query as well as easy to read

Prasad Telkikar · Accepted Answer · 2019-05-15 05:35:08Z

2

This is the shortest I can think of. Not sure if that makes the intent much clearer however.

list.Where(r => r.MyEnumValue == myEnum || (myEnum == MyEnum.B && r.MyEnumValue == MyEnum.A)).FirstOrDefault();

edited May 15, 2019 at 5:35

Prasad Telkikar

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answered May 15, 2019 at 5:30

Botz3000

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2 Comments

Shahar Shokrani Over a year ago

Hey @Botz, thanks, but in my taste it is still not clearer to maintain than the simple If else statement. See the updated question, I've also added C to compare with. I'm search for a design based solution.

Prasad Telkikar Over a year ago

why not !=, it will reduce linq query as well as easy to read

Prasad Telkikar · Accepted Answer · 2019-05-15 06:27:48Z

1

what about !=

 return list.Where(r =>
                        r.MyEnumValue != MyEnum.Undefined  || 
                        r.MyEnumValue != MyEnum.D
                    ).FirstOrDefault();

In real case we can take less elements in lookFor array and use negation, something like

var lookFor = new [] { MyEnum.Undefined, MyEnum.D};
return list.FirstOrDefault(r => !lookFor.Contains(r.MyEnumValue));

Please check negation in FirstOrDefault query, this will help us to reduce elements in loofFor array

edited May 15, 2019 at 6:27

answered May 15, 2019 at 5:43

Prasad Telkikar

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2 Comments

Shahar Shokrani Over a year ago

Good answer, but for me working with != is less intuitive to understand but still upvoted.

Prasad Telkikar Over a year ago

Agreed.. happy coding

Shahar Shokrani · Accepted Answer · 2019-05-15 06:13:56Z

0

Ended up mixing @john-wu and @botz3000 answers with:

var lookFor = new [] { MyEnum.A, MyEnum.B, MyEnum.C };

list.FirstOrDefault(r => r.MyEnumValue == myEnum || (
                             myEnum == MyEnum.B && lookFor.Contains(r.MyEnumValue)
                         )
                    );

answered May 15, 2019 at 6:13

Shahar Shokrani

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3 Comments

Prasad Telkikar Over a year ago

why not !=, it will reduce linq query as well as easy to read

Shahar Shokrani Over a year ago

Its true in the case of the simplified question, but in the real code there are many enum options

Prasad Telkikar Over a year ago

I updated my answer as you mentioned in above comments

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