Some basic data structures in Matlab

John Kitchin

There are a variety of needs for storing complicated data in solving engineering problems.

Contents

cell arrays

A cell array can store a variety of data types. A cell array is enclosed by curly brackets. Here, we might store the following data in a variable to describe the Antoine coefficients for benzene and the range they are relevant for [Tmin Tmax]

c = {'benzene' 6.9056 1211.0 220.79 [-16 104]}

c = 

    'benzene'    [6.9056]    [1211]    [220.7900]    [1x2 double]

To access the elements of a cell array use curly brackets for indexing.

c{1}

ans =

benzene

you can also index the cell array, e.g. to get elements 2-4:

[A B C] = c{2:4}

A =

    6.9056


B =

        1211


C =

  220.7900

If you want to extract all the contents to variable names that are easy to read, use this syntax:

[name A B C Trange] = c{:}

name =

benzene


A =

    6.9056


B =

        1211


C =

  220.7900


Trange =

   -16   104

structures

a structure contains named fields that can contain a variety of data types. Structures are often used to set options

s = struct('name','benzene','A',6.9056,'B',1211.0')

s = 

    name: 'benzene'
       A: 6.9056
       B: 1211

And you can add fields like this:

s.C = 220.79
s.Trange = [-16 104]

s = 

    name: 'benzene'
       A: 6.9056
       B: 1211
       C: 220.7900


s = 

      name: 'benzene'
         A: 6.9056
         B: 1211
         C: 220.7900
    Trange: [-16 104]

we can access the data in a struct by the field

s.name
s.Trange

ans =

benzene


ans =

   -16   104

It is an error to access a non-existent field, so you can check if it exists like this.

if isfield(s,'field3')
    s.field3
else
    'no field 3 found'
end

ans =

no field 3 found

Not sure what fields are in the struct? This might be the case for a struct returned by a Matlab function, e.g. by an ode solver or optimization algorithm.

fieldnames(s)

ans = 

    'name'
    'A'
    'B'
    'C'
    'Trange'

containers.Map

A container.Map is like a dictionary, with a key:value relationship. You can use complicated key strings including spaces. By default, all keys must be the same type, e.g. all strings.

cM = containers.Map();
cM('name') = 'benzene';
cM('A') = 6.9056;
cM('B') = 1211.0;
cM('C') = 220.79;
cM('Trange') = [-16 104];
cM('key with spaces') = 'random thoughts';

and we can access the data in a map by key:

cM('name')
cM('key with spaces')

ans =

benzene


ans =

random thoughts

it is also an error access a non-existent key, so we can check if it exists like this.

if cM.isKey('tre')
    cM('tre')
else
    'no tre key found.'
end

ans =

no tre key found.

Summary

These are a few of the ways to store/organize data in matlab scripts/functions.

% categories: basic

Published with MATLAB® 7.12