Output Structure Values Of Unequal Length To A Matrix

Lets say I have a structure (st) of of three runs depicted below which contains the following fields: run, x and y. run is only a scalar and x & y are the same length for each corresponding run. The following code is an example

st(1).run = 1; st(1).x = [0:2]'; st(1).y = 1*st(1).x;

st(2).run = 2; st(1).x = [5:7]'; st(2).y = 2*st(2).x;

st(3).run = 3; st(1).x = [0:2]'; st(3).y = 3*st(3).x;

I can generate the output that combines the entire structure into one matrix by using the following code which works

rightOutputMat = [];

for i = 1:length(s)

tempRun = ones(length(st(i).x),1)*st(i).run;

rightOutputMat = [rightOutputMat; tempRun st(i).x st(i).y];

end

However is it possible to generate an output vector without using a for loop. For example i can use the following to concatenate st.x & st.y into one matrix

outputMat = [vertcat(st.x) vertcat(st.y)];

but I am struggling to include the run number since it is only a scalar with length of 1 and x & y are the same lengths for

Thanks

Answer 1

[Deepak]

Hi @Michael Mancini,

To my understanding, you have created a structure that contains three fields: “run”, “x”, and “y”. Now, you want to combine the entire structure into one matrix without explicitly using a “for” loop.

To accomplish this task, we can use “repmat” and “arrayfun” functions in MATLAB to replicate and concatenate the scaler value “run”, converting it into a cell array containing row vectors of dimension 3x1. Now that all three fields of the structure have same dimensions, we can concatenate them into one matrix by using “vertcat” function.

Below is the complete MATLAB code that solves the task:

% Define the structure array
st(1).run = 1; st(1).x = (0:2)'; st(1).y = 1 * st(1).x;
st(2).run = 2; st(2).x = (5:7)'; st(2).y = 2 * st(2).x;
st(3).run = 3; st(3).x = (0:2)'; st(3).y = 3 * st(3).x;

% Use arrayfun to replicate the run number and concatenate results
runColumn = arrayfun(@(s) repmat(s.run, length(s.x), 1), st, 'UniformOutput', false);
outputMat = [vertcat(runColumn{:}), vertcat(st.x), vertcat(st.y)];

% Display the result
disp('Output Matrix:');

Output Matrix:

disp(outputMat);

     1     0     0
     1     1     1
     1     2     2
     2     5    10
     2     6    12
     2     7    14
     3     0     0
     3     1     3
     3     2     6

Please find attached the documentation of functions used for reference:

Arrayfun: www.mathworks.com/help/matlab/ref/arrayfun.html

Repmat: www.mathworks.com/help/matlab/ref/repmat.html

Vertcat: www.mathworks.com/help/matlab/ref/double.vertcat.html

I anticipate this will solve the problem.

[Voss]

Another option:

st(1).run = 1; st(1).x = (0:2).'; st(1).y = 1 * st(1).x;
st(2).run = 2; st(2).x = (5:7).'; st(2).y = 2 * st(2).x;
st(3).run = 3; st(3).x = (0:2).'; st(3).y = 3 * st(3).x;

outputMat = [repelem(vertcat(st.run),arrayfun(@(s)numel(s.x),st),1) vertcat(st.x) vertcat(st.y)]

outputMat = 9x3

1 0 0 1 1 1 1 2 2 2 5 10 2 6 12 2 7 14 3 0 0 3 1 3 3 2 6

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