Concatenate into a matrix is not saving and is overriding every iteration?

Question

nines 2022-6-14

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1740105-concatenate-into-a-matrix-is-not-saving-and-is-overriding-every-iteration

编辑： Matt J 2022-6-14

I have 2 subjects where each subject has three conditions. I made an array where each row is 1*3 representing one subject with the three conditions. I now want to add each subjects' array together.

However, my code seems to be overwriting every round, when I want:

%subject 1
percent_change = [1 2 3]
%subject 2
percent_change = [3 4 5]
%what I want as ouput:
percent_change_matrix: 1 2 3
                       3 4 5

Here is what I have tried:

%try 1
subjs = {'subject1' 'subject2'}
time = {'30-50' '50-60' '60-70'}
%% defining tac components for pet plot 
for s = 1:length(subjs)
    subj = subjs{s}
for i = 1:length(time)
        time = time{i}
        percent_change(:,i) = ((task-baseline)/baseline)*100 %task=2 baseline=1
end
percent_change_matrix = []
percent_change_matrix = [percent_change_matrix; percent_change]
end

I have also tried:

%try 2
subjs = {'subject1' 'subject2'}
time = {'30-50' '50-60' '60-70'}
%% defining tac components for pet plot 
for s = 1:length(subjs)
    subj = subjs{s}
for i = 1:length(time)
        time = time{i}
        percent_change(:,i) = ((task-baseline)/baseline)*100
end
try
percent_change_matrix = [percent_change_matrix; percent_change]
catch
percent_change_matrix = [percent_change_matrix]
end
end

my output for try 1 and try2 is:

percent_change_matrix: [3 4 5]

There are no errors with eithor of my codes, but the matrixes are not being built upon eachother. Do you have any suggestions? Thanks so much!

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nines 2022-6-14

编辑：nines 2022-6-14

task and baseline are each going to be equal to one number for each subject and time combination:

here are examples:

subject 1, time 30-50: task: 2, baseline: 1

subject 1, time 50-60: task: 3, baseline: 2

subject 1, time 60-70: task: 3, baseline: 2

subject 2, time 30-50: task: 2, baseline: 1

subject 2, time 50-60: task: 4, baseline: 3

subject 2, time 60-70: task: 5, baseline: 2

Ganesh 2022-6-14

在 MATLAB Online 中打开

The issue is that percent_change_matrix is being redefined to an empty array at every iteration for subject. Move the declaration of this to the beginning, or immediately following 'time' variable.

Another issue that may arise seems to be

time = time{i}

This would redefine your time variable. Consider naming one of the variables differently.

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Answer 1

Matt J 2022-6-14

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1740105-concatenate-into-a-matrix-is-not-saving-and-is-overriding-every-iteration#answer_985410

编辑：Matt J 2022-6-14

在 MATLAB Online 中打开

Ns=numel(subjs); Nt=numel(time);
percent_change=cell(Ns,1);
for s = 1:Ns
   subj = subjs{s};
    for i = Nt:-1:1
            ...
            percent_change{s}(:,i) = ((task-baseline)/baseline)*100 %task=2 baseline=1
    end
end
percent_change_matrix=cell2mat(percent_change);