3.4: Common Vector Operations

Once we create vectors, we often need to combine them, access or delete certain elements, or change values inside them.

Concatenating Vectors

Concatenation means joining arrays together. For row vectors, we can place two vectors next to each other inside square brackets.

Example \(\PageIndex{1}\)

 

Concatinating vectors. 

array3 = 1:5;
array4 = 9:-2:1;
catArray = [array3 array4]

Solution

The result is one longer row vector containing the values of array3 followed by the values of array4.

catArray =

1 2 3 4 5 9 7 5 3 1

 

 

Accessing Elements by Index

Each element in a vector has an index, which tells us its position. MATLAB indexing starts at 1. This is important: the first element is element 1, not element 0.

 

Example \(\PageIndex{2}\)

Accessing elements.

array3 = 1:5;
arr_1 = array3(5) % returns the 5th element
arr_2 = array3([1 3 5]) % returns the 1st, 3rd, and 5th elements
arr_3 = array3(1:3) % returns the 1st through 3rd elements

 

Solution

arr_1 =

     5


arr_2 =

     1     3     5


arr_3 =

     1     2     3

 

 

Caution

Common mistake: Students with experience in languages such as Python, C, or Java sometimes try to use index 0. MATLAB starts counting at 1.

 

Changing an Element

To change a value stored in a vector, refer to its index and assign a new value.

 

Example \(\PageIndex{3}\)

Changing an element.

array3 = 1:5;
array3(5) = 100

 

Solution

array3 =

     1     2     3     4   100

 Now the fifth element of array3 is no longer 5; it is 100.