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Working with Arrays in MATLAB



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mal appstores all types of data and

arrays this includes not only numeric

data but data of other types such as

strings or even complex objects so

working with arrays is fundamental to

working with MATLAB with the MATLAB

language you can create arrays access

and assign values to array elements

using a number of indexing methods and

perform many other operations to

manipulate the Rays contents let's first

look at creating arrays you can grain

ray by specifying specific values using

square brackets and commas or spaces to

separate columns in a row such as a

equals one two three four and semicolons

to separate rows you can create equally

spaced one-dimensional arrays with a

colon operator such as a equals 1 to 10

a equals 1 to 10 in steps of 2 or a

equals 10 to 1 and steps of negative 2

the lens space function is similar to

the colon operator letting you specify a

start and end value but gives control

over the number of points such as 7 you

can change the rows to columns with the

transpose operator you can also call a

number of functions that generate

elementary matrices with different

contents such as ones zeros or random

numbers

you

it can be more convenient to inspect the

contents of an array by opening it into

the variable editor let's now look at

how you can access and change the values

of array elements with different forms

of indexing you can specify elements of

array by simple row and column indexing

here is the element of a in the first

row second column you can specify a

range of rows and columns to access

sections of an array such as row 1

columns 1 through to the elements do not

have to be contiguous such as Row 1

columns 1 and 3 you can specify all rows

or columns by using the colon operator

in this case specifying all columns you

can also use the end keyword such as Row

1 columns 2 to the end or 2 to the N

minus 1

you can assign values to specific

elements by specifying indexing on the

left hand side of the equation such as

rows 1 columns 2 to the n minus 1 equals

1010 you can delete one or more rows of

an array such as rows 1 to 2 all the

columns by assigning them to the empty

matrix denoted by square brackets a is

now two rows shorter sometimes it is

convenient to treat two-dimensional

arrays such as these as a

one-dimensional array as though all the

columns were stacked together into a

single column and specify single index

this is called linear indexing for

example the element at Row 1

column-two can we access through one

linear index v this is possible because

matlab arrays are stored column wise

memory in other words each column in the

array is stored one after another so the

element at row one column two is in fact

the fifth element stored the colon

operator used on its own specifies all

elements when using linear indexing and

it returns a single column vector with

the entire array contents you can also

access elements with what is known as

logical indexing where you specify an

indexing array of equal size filled with

true or false values like a mask this is

useful for operating on elements whose

values match some criterion such as a is

less than 0.5 which creates an array of

logical values the same size as a with

true values displayed here as 1 whenever

a is less than 0.5 no logical values

like true and false

our displayed as one is zeros

respectively we can use logical arrays

such as this to perform logical indexing

such as set the elements of a where a is

less than 0.5 to negative 1 to find the

indices of array elements that magic

criteria use the find function which

finds nonzero values together with a

logical expression this gives the linear

indices of the elements that meet the

condition a is less than 0.5 you can get

the rows and column indices instead

you can see information about all

indexing techniques in the documentation

and finally let's look at how you can

extract some useful information about an

array and perform some basic operations

you can get basic information on an

array such as determine if it's empty

get the length usually used for 1d

arrays size of all the dimensions or the

total number of elements as we saw

before creating arrays with square

brackets lets us concatenate a number of

race together horizontally or vertically

other useful array manipulation

functions include flip left-right and

flip up/down rap mat to replicate

matrices reshape and sort

although the examples shown here use one

and two dimensional arrays most of these

techniques can be applied to

multi-dimensional arrays as well see the

documentation for more information this

concludes the demonstration try these

features in MATLAB now or watch one of

the other videos