Lambda expressions are a powerful feature in many programming languages, including Java and C#. They allow us to write concise and elegant code for tasks that would otherwise be more complex. In this article, we will explore how we can use lambda expressions to conditionally get indexes of list items.
Let's start by understanding what a lambda expression is. It is an anonymous function that can be passed as a parameter or stored in a variable. It consists of a list of parameters, an arrow (->), and a body. The body can be a single expression or a block of code. Now, let's dive into how we can use lambda expressions to get indexes of list items.
Suppose we have a list of numbers and we want to get the indexes of all the even numbers in the list. Traditionally, we would have to write a for loop and check each element for its evenness. However, with lambda expressions, we can achieve the same result in a more concise way.
First, we define a lambda expression that takes in a number and returns a boolean value indicating whether the number is even or not. This can be done using the modulus operator (%). If the number is divisible by 2, it is even, and the expression will return true, otherwise, it will return false.
Next, we use the built-in function 'filter' to filter out the even numbers from the list. The 'filter' function takes in a lambda expression and a list, and returns a new list with only the items that satisfy the given condition. In our case, it will return a list of even numbers.
But what about the indexes? Here comes the 'enumerate' function to the rescue. This function takes in a list and returns an iterable of tuples, where each tuple contains the index and the corresponding element in the list. By using the 'enumerate' function, we can get the indexes of the items in the filtered list.
Let's take a look at the code:
```
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
List<Integer> evenNumbers = numbers.stream()
.filter(n -> n % 2 == 0)
.collect(Collectors.toList());
List<Integer> evenIndexes = StreamUtils.enumerate(evenNumbers)
.map(tuple -> tuple.getIndex())
.collect(Collectors.toList());
```
In the above code, we first create a list of numbers using the 'Arrays' class. Then, we use the 'stream' method to convert the list into a stream, which allows us to use lambda expressions. Next, we use the 'filter' function to filter out the even numbers and collect the result into a list.
Finally, we use the 'enumerate' function from the 'StreamUtils' class to get the indexes of the even numbers. The 'map' function is used to extract the indexes from the tuples, and the 'collect' function collects the indexes into a list.
By using lambda expressions, we were able to achieve our goal in just a few lines of code. This not only makes our code more concise but also easier to read and maintain.
In conclusion, lambda expressions are a powerful tool for writing clean and efficient code. They allow us to perform complex tasks in a concise and elegant manner. In this article, we saw how we can use lambda expressions to conditionally get indexes of list items. So, next time you encounter a similar problem, don't forget to use the power of lambda expressions.
