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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
