How to concatenate vectors using append() or extend() in Rust

Vectors in the Rust programming language usually refer to dynamic arrays that allow us to store data with the same data type and insert new elements at runtime. The concatenation of these vectors helps us in combining and transforming data within Rust programs. In this Answer, we’ll discuss two methods, append() and extend(), to concatenate vectors in Rust.

The append() method

The append() method allows us to append the second vector to the first one. After performing this operation, the first vector contains elements of the second vector at the end, and the second vector becomes empty.

The syntax for the append() method is given below:

vec1.append(&mut vec2)

The append() method takes the mutable referenceIn Rust, a mutable reference is a reference to a variable or data structure that allows us to modify the data it references. Mutable references are a core concept in Rust’s ownership system and play a crucial role in enforcing memory safety and preventing data races in concurrent programming. of the second vector as an argument, which is why we used & with vec2. Let’s see how it works in the example given below:

fn main() {



   let mut my_vec1 = vec![9,8,7,6];

   let mut my_vec2 = vec![55,44,33,22];



   my_vec1.append(&mut my_vec2);

     

   print!("my_vector1 : ");     

   for i in my_vec1  

   {  

       print!("{} ",i);  

   }  



}

Code explanation

Let’s discuss the above code snippet in detail.

  • Lines 3–4: We use the let and mut keywords to declare the mutable vectors, such as my_vec1 and my_vec2.

  • Line 6: The append() method takes the reference of my_vec2 vector.

  • Lines 8–12L: The for loop is used to print the values of my_vec1 that include values of my_vec2 vector as well.

As we’ve seen, the append() method concatenates vectors in place. Now, let’s move on to the next method that concatenates the vectors without taking the mutable references of another vector.

The extend() method

The extend() method concatenates vectors directly, taking an iterable vector rather than a reference to a vector. This method copies all elements to the first vector and appends them in the order they appear in the second vector. The good thing about the extend() method is that it doesn’t empty the second vector.

The syntax for the extend() method is given below:

vec1.extend(iterable)

The extend() method takes the second vector as an argument and updates the first vector. Let’s see how it works in the example given below:

fn main() {



   let mut my_vector1 = vec![9,8,7,6];

   let my_vector2 = vec![5,4,3,2];



    my_vector1.extend(my_vector2);



   print!("my_vector1 : ");     

   for i in my_vector1  

   {  

       print!("{} ",i);  

   }   



}

Code explanation

Let’s discuss the code snippet above in more detail.

  • Lines 3–4: We use the mut keyword only with my_vector1 to make it mutable.

  • Line 6: The extend() method takes my_vector2 as a vector iterator. It iterates each element of my_vector2 and appends them to my_vector1.

Let’s summarize both approaches by seeing their differences, as shown in the table below:


The append()Method

The append()Method

Description

Moves the second vector to the first vector

Appends the elements of second vector to the first vector

Usecase

Doesn’t need a second vector

Needs a second vector

Usage

vec.append(&mut vec2)

vec.append(iterable)

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