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College of EngineeringEngineering Education Innovation Center

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Array Accessing and Strings in MATLAB

Topics Covered:

1. Array addressing.

2. Character arrays.

Creating Arrays / Chapter 2

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ARRAY ADDRESSING (VECTOR)

The address of an element in a vector is its position in the row (or column), starting at 1.

>> v = [35 46 78 23 5 14 81 3 55]v = 35 46 78 23 5 14 81 3 55

>> v(4) ans = 23

>> v(7) ans = 81

>> v(1) ans = 35

It is possible to change an element in a vector by entering a value to a specific address directly:

>> v(6) = 273v = 35 46 78 23 5 273 81 3 55

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Addressing Specified Elementsof a Vector

Any combination of elements from a vector can be addressed in any order

>> v = [4 15 8 12 34 2 50 23 11]

v =

4 15 8 12 34 2 50 23 11

>> u = v([4 5 7 3 3])

u =

12 34 50 8 8

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v([4 5 7 3 3]) is the same as ( [v(4), v(5), v(7), v(3), v(3)] ).

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USING A COLON (:) WHEN ADDRESSING VECTORS

The colon operator can be used to generate a list of elements to address

All the elements of a vector (either a row vector or a

column vector)

Elements 3 through 7 ( [v(3), v(4), v(5), v(6), v(7)] ).

>> v = [4 15 8 12 34 2 50 23 11]

v =

4 15 8 12 34 2 50 23 11

>> u = v(3:7)

u =

8 12 34 2 50

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v(:)

v(3 : 7)

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ARRAY ADDRESSING (MATRIX)

>> m=[3 11 6 5; 4 7 10 2; 13 9 0 8]

m =

3 11 6 5

4 7 10 2

13 9 0 8

>> m(1,1)

ans =

3

>> m(2,3)

ans =

10

35

Single elements can be used like variables in computations:

>> m(2,3) - m(1,1)ans = 7

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USING A COLON (:) WHENADDRESSING MATRICES

A(: , 3)

A(2 , :)

A(: , 2:5)

A(2:4, :)

A(1:3, 2:4)

A([4 2],:)

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Elements in all the rows of column 3

Elements in all the columns of row 2

Elements in columns 2 through 5 in all the rows

Elements in rows 2 through 4 in all the columns

Elements in rows 1 through 3 and in columns 2

through 4

Elements in all the columns of rows 4 then 2

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ADDRESSING MATRICES

>> A = [1 3 5 7 9; 2 4 6 8 10;

3 6 9 12 15; 4 8 12 16 20;

5 10 15 20 25]

A =

1 3 5 7 9

2 4 6 8 10

3 6 9 12 15

4 8 12 16 20

5 10 15 20 25

>> B = A(:,3)

B =

5

6

9

12

15

>> C = A(2,:)

C =

2 4 6 8 10

Define a matrix

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Define a matrixusing part of A

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ADDRESSING MATRICES

>> D = A(:, 2:5)

D =

3 5 7 9

4 6 8 10

6 9 12 15

8 12 16 20

10 15 20 25

>> F = A(1:3,2:4)

F =

3 5 7

4 6 8

6 9 12

>> E = A(2:4,:)

E =

2 4 6 8 10

3 6 9 12 15

4 8 12 16 20

A =

1 3 5 7 9

2 4 6 8 10

3 6 9 12 15

4 8 12 16 20

5 10 15 20 25

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>> G = A([5 2],5:-2:1)

G =

25 15 5

10 6 2

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ADDRESSING MATRICES

>> A(1:2,1:3) = B([5 5],2:4)

A = 10 15 20 0 0

10 15 20 0 0

0 0 0 0 0

0 0 0 0 0

>> A = zeros (4,5)

A =

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0

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B =

1 3 5 7 9

2 4 6 8 10

3 6 9 12 15

4 8 12 16 20

5 10 15 20 25

>> A(3:4,[1 4 5]) = B(1:2,1:3)

A = 10 15 20 0 0

10 15 20 0 0

1 0 0 3 5

2 0 0 4 6

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Strings are a special case of a vector (row array) where every element is a character.

Strings are created by entering the characters between single quotes.

String arrays can include letters, digits, other symbols, and spaces

Examples of strings: 'ad ef ', '3%fr2', '{edcba :21!'

Character Arrays

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STRING VARIABLES

>> a = 'ERty 8'

a =

ERty 8

>> B = ['My name is John Smith']

B =

My name is John Smith

a has 6 elements, and B has 21 elements

The elements can be addressed like any other row array

>> a(4)

ans =

y

>> B(12)

ans =

J

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STRING VARIABLES

>> x = 536

x =

536

>> x = '536'

x =

536

The string variable:

is not the same as the number variable:

If you use a string variable in calculations, you get an answer based on the ascii storage code for those characters (probably not what you wanted)!

An important application of strings is in creating input prompts and output messages. This will be shown later when script file I/O (input/output) is discussed.

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