Loop through IEnumerable using Lambda

Question

I have a func which looks like below

Func<Product, bool> ItemProduct(Iitem item) => (pro)=> pro.ItemID == item.Id;

I am looking for a func which take multiple items. I am trying like below but that is not correct...Can you please help me how to do this?

Func<Product, bool> ItemProduct(IEnumerable<Iitem> items) => (pro) => pro.ItemID == items.Id;

What is `ItemProduct(IEnumerable items)` expected to do/return? — Yacoub Massad, May 25 '17 at 14:18
Indeed - providing a [mcve] would really clarify this, and in coming up with it you may well answer your own question. — Jon Skeet, May 25 '17 at 14:20
@reddy Do you want to return a function that returns true if *all* ids match, or if *any* id matches? — 15ee8f99-57ff-4f92-890c-b56153, May 25 '17 at 14:28
What do you mean by "that is not correct". What exact problem are you facing? — Siva Gopal, May 25 '17 at 14:29
Shouldn't it be `Func, bool> ItemProduct(IEnumerable items)...`. Give it a try. — Siva Gopal, May 25 '17 at 14:30
@Ed Plunkett I am expecting to return all ids match should be retuned — reddy, May 25 '17 at 14:32
@reddy Are you saying that you want to return a function which returns `true` if ALL ids match? — 15ee8f99-57ff-4f92-890c-b56153, May 25 '17 at 14:33
@SivaGopal i think you are correct i think it should be Func, bool> ItemProduct(IEnumerable items) — reddy, May 25 '17 at 14:33
@reddy So you want to return `Func>`? The *second* type argument is what the function will return. — 15ee8f99-57ff-4f92-890c-b56153, May 25 '17 at 14:41

15ee8f99-57ff-4f92-890c-b56153 · Answer 1 · 2017-05-25T16:05:18.777

From comments, it may be that you actually want to generate a function that will own an enumeration of Iitem and take a Product as a parameter, and will return all of its Iitems whose Id matches the ItemID of the Product. That's this:

Func<Product, IEnumerable<Iitem>> ItemProduct(IEnumerable<Iitem> items) =>
    pro => items.Where(item => pro.ItemID == item.Id);

Used like so:

var someItems = new [] { new Iitem { Id = 1 }, new Iitem { Id = 2 } };

var f = ItemProduct(someItems);

var prod = new Product { ItemID = 1; }

//  Results will be an enumeration that will enumerate a single Iitem, the 
//  one whose Id is 1. 
var results = f(prod);

I'll leave my original guess here, because I'm still not sure what you really want.

This method will return a func that returns true if all Ids in items match the ItemID of the Product passed in as a parameter:

Func<Product, bool> ItemProduct(IEnumerable<Iitem> items) =>
    (pro) => items.All(item => pro.ItemID == item.Id);

Like so:

var product = new Product() { ItemID = 1 };
var itemColl1 = new Iitem[] { new Iitem { Id = 1 }, new Iitem { Id = 2 } };
var itemColl2 = new Iitem[] { new Iitem { Id = 1 }, new Iitem { Id = 1 } };

var f1 = ItemProduct(itemColl1);
var f2 = ItemProduct(itemColl2);

bool thisWillBeFalse = f1(product);
bool thisWillBeTrue = f2(product);

If you want the function to return true if at least one of the Ids matches, but not necessarily all of them, this would do that. The only difference is that items.All() changes to items.Any():

Func<Product, bool> ItemProductAny(IEnumerable<Iitem> items) =>
    (pro) => items.Any(item => pro.ItemID == item.Id);

Like so:

var f3 = ItemProductAny(itemColl1);
var f4 = ItemProductAny(itemColl2);

bool thisWillAlsoBeTrue = f3(product);
bool thisWillAlsoBeTrueAgain = f4(product);


var itemColl3 = new Iitem[] { new Iitem { Id = 2 }, new Iitem { Id = 3 } };

var f5 = ItemProductAny(itemColl3);

bool butThisWillBeFalse = f5(product);

@reddy Great. You should accept it as the correct answer in that case. — 15ee8f99-57ff-4f92-890c-b56153, May 26 '17 at 11:06

score 1 · Answer 2 · answered May 25 '17 at 14:40

Assuming you need to return a function which for a given product returns true if all items from a given set have the same Id as the product's ItemID, you may use items.All(...) instead of single ID comparison:

Func<Product, bool> ItemProduct1(IEnumerable<Iitem> items) 
    => (pro) => items.All(i => pro.ItemID == i.Id);

If you need true for products which ItemID matches Id of just some of the given items, use items.Any(...) instead:

Func<Product, bool> ItemProduct1(IEnumerable<Iitem> items) 
    => (pro) => items.Any(i => pro.ItemID == i.Id);

Loop through IEnumerable using Lambda

2 Answers2