Array.Find with more parameters

Question

5.00/5 (2 votes)

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Hey everybody,

I find that using Array.Find is very useful in C#. I know it works like the following example:

C#

public void Main
{
String[] names = new String[4]     
{"john","mary","peter","justin");
String theone = Array.Find(names,MyCondition);
}

private Boolean MyCondition(String name)
{
return name.Lenght==5; //supposing that I want a name just with 5 letters
}

But I was wondering if I can send more parameters to 'MyCondition' (for example the lenght I am looking for). I tryed it and Visual Studio generated a new method like this:

C#

public void Main
{
String[] names = new String[5]     
{"john","mary","peter","justin");
int lenght = 5;
String theone = Array.Find(names,MyCondition(names, lenght));
}
private Predicate<String> MyCondition(String name, int lenght)
{
}

And I don't know what to do from here :~
Can you help me please how to use this new method I've never seen before? Or, What can I do if I want to send more parameters to a predicate than just one as a default method?

Posted 2-Feb-11 4:22am

pancho2413

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3 solutions

Solution 1

You can use the closure mechanism and an anonymous function and you won't have to pass anything in as it will be visible to the anonymous function. See here:

C#

public void Main
{
    String[] names = new String[5]{"john","mary","peter","justin");
    int length = 5;
    String theone = Array.Find(names,delegate(String name)
                                     {
                                          return name.Length == length;
                                     }
    );

}

Array.Find takes an array and a bool delegate(String x) method. That means a method that takes exactly one String parameter and returns bool. You can also use the Generic form if you need to pass something other than a String. length will not have to be passed as a parameter since it is visible to the anonymous method.

Anymore questions? Leave a comment.

Cheers!

Posted 2-Feb-11 4:40am

Manfred Rudolf Bihy

Updated 2-Feb-11 5:13am

v2

Comments

Sandeep Mewara 2-Feb-11 12:48pm

Great! 5+

Solution 2

You could pass your string[] array into a generic list constructor and use the .Find() method of the list with a lambda expression that checks for as many conditions as you please:

C#

public void Main
{
List<string> names = new List<string>(new String[4]{"john","mary","peter","justin"));

int length = 5;

String theone = names.Find(s => (s == "john" && s.Length == length));
}
</string></string>

You might be able to use a similar lambda expression with Array.Find(), but I don't know because I never use Array methods.

Posted 2-Feb-11 4:42am

jim lahey

Comments

Sandeep Mewara 2-Feb-11 12:48pm

Another good way! 5+

Manfred Rudolf Bihy 2-Feb-11 18:52pm

You get my 5 eventhough I must remark that "john" does not have a length of 5 and thus your Find call will return nothing. :)

jim lahey 3-Feb-11 3:29am

I guess "john" isn't "the one" after all :)

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dasblinkenlight · Accepted Answer · 2011-02-02T04:50:00

Solution 3

This may look like a bit of magic initially, yet this is what will ultimately do the job:

C#

public void Main() {
    var names = new[] { "john", "mary", "peter", "justin" };
    var lenght = 5;
    var theone = Array.Find(names, MyCondition(lenght));
}
private static Predicate<string> MyCondition(int lenght) {
    return s => s.Length == lenght;
}

The best way to understand what's going on here is to set a breakpoint on the line with the "return" statement, and run the program in the debugger. When you reach the breakpoint for the second time, open the call stack.

Posted 2-Feb-11 4:50am

dasblinkenlight

Comments

Sandeep Mewara 2-Feb-11 12:52pm

Great! 5+

Manfred Rudolf Bihy 2-Feb-11 18:49pm

Returning an anonymous method from a method, nice idea! 5+
I still prefer to define these lambdas inline though. The creation from within a method does make sense though for two reasons:
1. Encapsulation of the closure in local/parameter variables of the method
2. Reuse of the returned lambda is possile

dasblinkenlight 2-Feb-11 18:55pm

I just wanted to stay with the code template from the question as much as possible :)