C# Iterate through string with Linq .Select()-CodePudding

Why can't I iterate through a string and add the letters (chars) to a HashSet like in the example above.

I tried to execute this part of the code but the HashSet was empty. `

HashSet<char> chars2 = new HashSet<char>();
myString.Select(l => chars2.Add(l));

CodePudding user response：

Delayed/deferred execution! There is no need to evaluate the Select

If you add a ToList() to the end, it will execute your lambda and will add the items.

You can also change it to a ForEach

Knowing this, beware that if you do not a ToList() to it, and iterate your collection, it will execute it again and again, so if your Select is expensive to run, make sure to run it once.

CodePudding user response：

I'm not sure what the "example above" is, but you're using LINQ incorrectly. The Select method should not be used to create side effects. chars2.Add() creates a side effect.

In addition, most Linq methods are not executed if they don't need to be. This is called "Deferred Execution".

Instead, use a foreach, which is intended to create side effects while looping through elements.

var myString = "abcd";
HashSet<char> chars2 = new HashSet<char>();

foreach (var chr in myString)
{
    chars2.Add(chr);
}

There are also more direct ways to create a hash set from specifically a string

myString.ToHashSet()
new HashSet<char>(myString)

CodePudding user response：

Select is a LINQ method. Most LINQ methods are intermediate expressions and don't consume the collection. You must call a terminal operation such as ToList or ForEach to actually "execute" the query.

But note that using Select/ForEach to add to a set is a bit odd: you are using a functional approach to execute a side-effect (inherently non-functional!).

Instead, use ToHashSet() directly:

HashSet<char> chars2 = myString.ToHashSet();