CODEWITHSUNDEEP
matlabstruct
O_O
O_O

Reputation: 4477

Initializing structure in Matlab

I am trying to initialize a structure in MATLAB similar to how C code does

typedef struct{
 float x;
 float y;
} Data

Data datapts[100];

From MATLAB, I know this is how to create a structure:

Data = struct('x', 0, 'y', 0)

but how do you create 100 instances of it?

Or is this not usually done in MATLAB? Does MATLAB prefer dynamic allocation whenever there is new data to add?

Upvotes: 5

Views: 12462

Answers (4)

mcmuffin6o
mcmuffin6o

Reputation: 550

While each of the other answers are helpful, they don't actually address the question. If you would like to create a data structure that is only a blueprint until you instantiate it, you have to use a class.

Here's a class that will do the trick. Refer to the documentation for details on file structure.

classdef Data
  properties
    x = 0  % If you don't want to initialize upon instantiation,
    y = 0  % you could instead have x/y {mustBeNumeric}
  end
end

Then, instantiate it by calling dataPoint = Data and use repmat to make 100 as you desire.

Upvotes: 1

abcd
abcd

Reputation: 42225

I don't know C, so I don't know how your code initializes the structure. However, consider these two possibilities:

1. A struct array data with 100 elements, each of which has two fields x and y

You can initialize an empty struct with

data = struct('x', cell(100,1), 'y', cell(100,1));

and you access each element of the struct array as data(1) and each of these is a struct. Typically, these are used when you have several equivalent "things" with the same set of properties, but different values for each.

Example:

elements = struct(...
    'name',         {'Hydrogen', 'Helium', 'Lithium'},...
    'atomicWeight', {1, 4, 7}, ...
    'symbol',       {'H', 'He', 'Li'});

elements(1)
ans = 

        name: 'Hydrogen'
atomicWeight: 1
      symbol: 'H'

So you can access each individual struct to get to its properties. Now if you wanted to append a struct array with the next 10 elements to this list, you can use cat, just like you would for matrices.

2. A struct data with two fields x and y, each with 100 elements

You can initialize this as

data = struct('x',zeros(100,1),'y',zeros(100,1));

and you access each element of the field as data.x(1). This is typically used when you have one "thing" with several properties that can possibly hold different values.

Example:

weather=struct('time',{{'6:00','12:00','18:00','24:00'}},...
    'temperature',[23,28,25,21]);

Once you understand structs and struct arrays and how they're used and indexed, you can use them in more complicated ways than in the simple illustration above.

Upvotes: 14

Nzbuu
Nzbuu

Reputation: 5251

In addition to the other methods described by @yoda and @Jacob, you can use cell2struct.

Upvotes: 1

Jacob
Jacob

Reputation: 34601

repmat(Data,100,1);

You can assign data to it with:

Data(1).x = 10;
Data(1).y = 20;

Upvotes: 5

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