Custom LINQ extension methods in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an extension method that returns the first element of a sequence.

C Sharp (C#)

public static T [1]<T>(this IEnumerable<T> source) {
    foreach (var item in source) {
        return item;
    }
    throw new InvalidOperationException("Sequence contains no elements");
}

Drag options to blanks, or click blank then click option'

AFirst

BSelect

CWhere

DOrderBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using a LINQ method name that does not return a single element.

Forgetting to make the method an extension method with 'this' keyword.

The method name First is used to get the first element in a sequence.

2fill in blank

medium

Complete the code to define an extension method that filters elements based on a predicate.

C Sharp (C#)

public static IEnumerable<T> [1]<T>(this IEnumerable<T> source, Func<T, bool> predicate) {
    foreach (var item in source) {
        if (predicate(item)) {
            yield return item;
        }
    }
}

Drag options to blanks, or click blank then click option'

ASelect

BOrderBy

CWhere

DGroupBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Select' which transforms elements instead of filtering.

Not using 'yield return' to return filtered elements lazily.

The method Where filters elements based on a condition (predicate).

3fill in blank

hard

Fix the error in the extension method that projects each element to a new form.

C Sharp (C#)

public static IEnumerable<TResult> Select<T, TResult>(this IEnumerable<T> source, Func<T, TResult> selector) {
    foreach (var item in source) {
        yield return [1];
    }
}

Drag options to blanks, or click blank then click option'

Aitem

Bselector(item)

Csource

Dselector

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the item itself instead of applying the selector.

Returning the selector delegate instead of calling it.

The Select method applies the selector function to each item and returns the result.

4fill in blank

hard

Fill both blanks to create an extension method that counts elements matching a condition.

C Sharp (C#)

public static int Count<T>(this IEnumerable<T> source, Func<T, bool> predicate) {
    int count = 0;
    foreach (var item in source) {
        if (predicate(item) [1] true) {
            count [2] 1;
        }
    }
    return count;
}

Drag options to blanks, or click blank then click option'

A=>

B==

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=>' which is not a comparison operator.

Using '-=' which decreases the count incorrectly.

The condition uses == to check if predicate returns true, and += increments the count.

5fill in blank

hard

Fill both blanks to create an extension method that returns a dictionary with keys and values selected from the source.

C Sharp (C#)

public static Dictionary<TKey, TValue> ToDictionary<TSource, TKey, TValue>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TValue> valueSelector) {
    var dict = new Dictionary<TKey, TValue>();
    foreach (var item in source) {
        dict.[1](keySelector(item), [2]);
    }
    return dict;
}

Drag options to blanks, or click blank then click option'

AAdd

BvalueSelector(item)

Citem

DRemove

Attempts:

3 left

💡 Hint

Common Mistakes

Using Remove instead of Add.

Passing the item directly instead of the selected value.

The method Add inserts a key and value into the dictionary. The value is obtained by calling valueSelector(item).