MATLAB: Structures

structures

I have loaded data that contain structures. The structures are of the form I have variable : struct1, struct2, struct3…. I have a 'file' with the list of these variables and want to manipulate the data contained in the structures with a for-loop.

Here is what I did:

      for i = 1:numel(files)
           data = files(i).data or data{1}.data
      some code;
end

I have errors like : Improper index matrix reference and other errors, Cell contents reference from a non-cell array object.

Best Answer

You could have the following structure:

s.myfield = 10;
s.another = 20;
s.hello   = 30;

Now suppose you have a list with the fieldnames which also happens to be the function to retrieve them from a structure:

fnames = {'myfield','another','hello'};

(Note that I didn't call the list with the name of the function)

Now you can manipulate the structure using dynamic fieldname indexing:

for n = 1:numel(fnames)
    tmp = s.(fnames{n});
    % do stuff with tmp or directly with s.(fnames{n}) 
end

This is a complete reference to manipulate structures: structures

Related Solutions

MATLAB: Make a table from a structure

I figured it out ! Apparently the field name should be set to x_T before inserting the variables to the table.

fnames = fieldnames(data);
T = table;
for i = 1:length(fnames)
    x_T = table(num2cell(getfield(data, fnames{i})));
    x_T.Properties.VariableNames = {fnames{i}};
    T = [T, x_T];
end

MATLAB: Multiplying structures together based on field names

A function to multiply two structures field by field. This needs to be copied into a file on your MATLAB path called multiplyStructs.m

function s3 = multiplyStructs(s1, s2)
%MULTIPLYSTRUCTS multiplies structures field by field
%   S3 = MULTIPLYSTRUCTS(S1, S2) returns a structure S3 with those fields
%   that are common to S1 and S2. The value of each such field is the
%   matrix product of the values of the corresponding fields of S1 and S2.
% get common field names
f1 = fieldnames(s1);
fnames = f1(ismember(f1, fieldnames(s2)));
% multiply
for k = 1:length(fnames)
    fname = fnames{k};
    s3.(fname) = s1.(fname) * s2.(fname);   % matrix product
end
end

Test code:

struct1.a = 1;
struct1.b = 2;
struct1.c = 3;  % will be ignored as no match
struct1.d = 4;
struct2.a = 3;
struct2.b = 4;
struct2.d = 10;
struct3 = multiplyStructs(struct1, struct2)

An alternative way, which works only if all the structures have the same fields, but which generalises more readily to multiple structures, is to use this function:

function s = structProd(svec)
%STRUCTPROD returns the field-by-field products of a structure array
%   S = STRUCTPROD(SARR) takes a structure array and returns a scalar
%   structure with the same fields. The value of each field of S is the
%   product of the values of the corresponding fields of SARR, which must
%   all be numerical scalars.
%
%   See also: prod
fnames = fieldnames(svec);
for k = 1:length(fnames)
    fname = fnames{k};
    s.(fname) = prod([svec.(fname)]);
end
end

and then put the structures into an array (which indeed might be the best way to store them to start with. Here's the test code:

struct1.a = 1;
struct1.b = 2;
struct1.d = 4;
struct2.a = 3;
struct2.b = 4;
struct2.d = 10;
struct3.a = -1;
struct3.b = -1;
struct3.d = -1;
struct4.a = 4;
struct4.b = 1;
struct4.d = 2;
struct5 = structProd([struct1 struct2 struct3 struct4])

Best Answer

Related Solutions

MATLAB: Make a table from a structure

MATLAB: Multiplying structures together based on field names

Related Question