Variables within lambda/LINQ

Question

is there a way for bellow lambda expression to move the method call ConvertFilterType(filter.FilterTypeId) into a variable so it is not called repeatedly for every condition ?

This if statement is making sure collection consist of all required filters.

if (run.Filters.All(
           filter => (ConvertFilterType(filter.FilterTypeId) != FilterType.A)
                  && (ConvertFilterType(filter.FilterTypeId) != FilterType.B)
                  && (ConvertFilterType(filter.FilterTypeId) != FilterType.C)
                  && (ConvertFilterType(filter.FilterTypeId) != FilterType.D)
                  && (ConvertFilterType(filter.FilterTypeId) != FilterType.E)))
    {
       throw new ArgumentException();
    }

you can use { } in a lambda expression

default
– default

2013-08-14 11:45:28 +00:00
Commented Aug 14, 2013 at 11:45 — default
– default, Commented Aug 14, 2013 at 11:45

King King · Accepted Answer · 2013-08-14 11:47:01Z

6

if (run.Filters.All(
       filter => {
              FilterType t = ConvertFilterType(filter.FilterTypeId);
              return
              t != FilterType.A && t != FilterType.B && t != FilterType.C && t != FilterType.D && t != FilterType.E;                        
         }))
   {
    throw new ArgumentException();
   }

answered Aug 14, 2013 at 11:47

King King

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Comments

brader24 · Accepted Answer · 2013-08-14 11:59:14Z

3

King beat me to it. Although it is not what you asked, I would also recommend that for improved readability, that you create a separate method with a more meaningful name. This chain of logic can obscure the intent of what you are doing. Extracting it into a method would help clarify the method's intent. I would have put this in the comment's to King's post, but don't have the reputation yet.

Here is some sample code, though I don't know what the type of the items in your Filters collection to know what the parameter of the method would need to be.

   if (run.Filters.All(filter => { return IsFilterAllowed(filter); } )
   {
       throw new ArgumentException();
   }

    private bool IsFilterAllowed(FiltersItemType filter)
    {
        FilterType t = ConvertFilterType(filter.FilterTypeId);
        return
              t != FilterType.A &&
              t != FilterType.B &&
              t != FilterType.C &&
              t != FilterType.D &&
              t != FilterType.E;
    }

edited Aug 14, 2013 at 11:59

answered Aug 14, 2013 at 11:50

brader24

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2 Comments

Vojtiik Over a year ago

This is a very good point ! Thx. I am sure you will gain your reputation soon.

brader24 Over a year ago

I just don't spend enough time on here contributing.

keyboardP · Accepted Answer · 2013-08-14 12:00:18Z

2

King's answer is the way to go but could you could also do this it seems.

FilterType[] notTheseFilters = new FilterType[] { FilterType.A, FilterType.B...};
bool result = !Filters.Any(f =>
                    notTheseFilters.Contains(ConvertFilterType(f.FilterTypeId)));

answered Aug 14, 2013 at 12:00

keyboardP

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Comments

default · Accepted Answer · 2013-08-14 12:03:49Z

0

If my logic serves me right, you could also do this

var filterTypesToAvoid = new[]{
     FilterType.A,
     FilterType.B,
     FilterType.C,
     FilterType.D,
     FilterType.E
};

if (run.Filters.All(
        filter => !filterTypesToAvoid.Contains(ConvertFilterType(filter.FilterTypeId))
    ))
    {
       throw new ArgumentException();
    }

This way there is no need for brackets in the LINQ query.

answered Aug 14, 2013 at 12:03

default

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Comments

Andrei · Accepted Answer · 2013-08-14 12:52:22Z

0

To extend what brader24 proposed, you could try :

 if (run.Filters.All(IsFilterAllowed))
 {
   throw new ArgumentException();
 }

private bool IsFilterAllowed(FiltersItemType filter)
{
    FilterType t = ConvertFilterType(filter.FilterTypeId);
    return
          t != FilterType.A &&
          t != FilterType.B &&
          t != FilterType.C &&
          t != FilterType.D &&
          t != FilterType.E;
}

answered Aug 14, 2013 at 12:52

Andrei

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