C#•17mo ago

❔ Anonymous function in LINQ Select

I have a code as following:

class Item {
    int price {get;set;}
}

bool showMax;
bool showMin;

if (showMax) 
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Max(y => y.Price), otherFields...));
else if (showMin)
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Min(y => y.Price), otherFields...));
else
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Average(y => y.Price), otherFields...));

class Item {
    int price {get;set;}
}

bool showMax;
bool showMin;

if (showMax) 
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Max(y => y.Price), otherFields...));
else if (showMin)
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Min(y => y.Price), otherFields...));
else
  var myLinqQuery = queryGroup.Select(x => new Item(price= x.Average(y => y.Price), otherFields...));

Is there a way to somehow pass just the LINQ Max/Min/Average function so I don't have to repeat the rest?

15 Replies

blueberriesiftheywerecats•17mo ago

chat gpt answer

class Item {
    int price { get; set; }
}

bool showMax;
bool showMin;

Func<IEnumerable<int>, int> aggregationFunction;

if (showMax)
    aggregationFunction = collection => collection.Max();
else if (showMin)
    aggregationFunction = collection => collection.Min();
else
    aggregationFunction = collection => (int)collection.Average();

var myLinqQuery = queryGroup.Select(x => new Item { price = aggregationFunction(x.Select(y => y.Price)), otherFields = ... });

class Item {
    int price { get; set; }
}

bool showMax;
bool showMin;

Func<IEnumerable<int>, int> aggregationFunction;

if (showMax)
    aggregationFunction = collection => collection.Max();
else if (showMin)
    aggregationFunction = collection => collection.Min();
else
    aggregationFunction = collection => (int)collection.Average();

var myLinqQuery = queryGroup.Select(x => new Item { price = aggregationFunction(x.Select(y => y.Price)), otherFields = ... });

Thinker•17mo ago

Is this EF?

popcornOP•17mo ago

Yes, EF6

Thinker•17mo ago

then no, you have to repeat it actually no wait

popcornOP•17mo ago

The chatgpt won't work? It looks promising

Thinker•17mo ago

lmao no I have no idea what that does EF can't translate arbitrary function invocations regardless

blueberriesiftheywerecats•17mo ago

maybe, but it might would want to work with queryGroup.ToList(), not just queryGroup

Thinker•17mo ago

Expression<Func<Item, int>> priceFunc = y => y.Price;
// ...
queryGroup.Select(x => new Item(price = x.Max(priceFunc), otherFields...));

Expression<Func<Item, int>> priceFunc = y => y.Price;
// ...
queryGroup.Select(x => new Item(price = x.Max(priceFunc), otherFields...));

this might work probably not though

blueberriesiftheywerecats•17mo ago

it might

Thinker•17mo ago

It would work on IEnumerable/List but certainly not on IQueryable Thing is that EF makes it difficult to factor out selectors and whatnot because it has to be able to translate the entire query.

popcornOP•17mo ago

I cast it to List anyways, so I think it might be okay to just do these Max/Min/Avg on the list instead in the query? Or I can do all 3 at the same time, but I really need just one of these based on the conditions so I was thinking it would cost performace for nothing.

Thinker•17mo ago

I'm no EF expert but I don't think you want to call .ToList() if you're gonna do more filters/maps on it.

popcornOP•17mo ago

Yea because after the .ToList() it won't be a SQL Query but just the LINQ filtering which is perhaps slower

Thinker•17mo ago

won't necessarily be slower, just won't act towards the database .ToList() executes the query synchonously and returns a list.

Accord•17mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Anonymous function in LINQ Select