How to plot data of only specified rows of matrix

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Anthony Koning
Anthony Koning 2023-4-11
评论： Star Strider 2023-4-11
Hi, I'm currently trying to plot a line from rows 1 and 7 of an 8*1000 single matrix from data imported from a .mat file, however, whenever I try to run it, Matlab keeps telling me there's some type of error in my plot arguement. If someone could explain to me what I'm doing wrong, that would be appreciated. Thank you very much. My sript is as follows:
y = load("data.mat");
figure
hold on
plot(y(1,:))
plot(y(7,:))

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回答（2 个）

VBBV
VBBV 2023-4-11
编辑：VBBV 2023-4-11
The load function imports data to a struct which contains the variables. To access them you need to use a dot operator, Shown here is a variable named Var1 contained in struct
y = load("data.mat");
figure
hold on
plot(y.Var1(1,:))
plot(y.Var1(7,:))
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Anthony Koning
Anthony Koning 2023-4-11
I unfortunately cannot currently upload the data.mat file. Additionally, loading the code you've adjusted just results in an error message of "Unrecognized field name "Var1"."
VBBV
VBBV 2023-4-11
编辑：VBBV 2023-4-11
Ran in:
Ok. That's because I don't have your data.mat file and the field variables inside that file may be differently named. To just show how it works, I have assumed it as Var1. To access the variable data and plot you can follow the code which I have shown but replace Var1 with name that's actually present in your data.mat file.
y.X = randi([0 8],8,1000); % random data with field variable X
hold on
plot(y.X(1,:))
plot(y.X(7,:))

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Star Strider
Star Strider 2023-4-11
Ran in:
It is straightforward to create ‘y’ to test the code —
y = randn(8,1000); % Create 'y'
save('data.mat', 'y') % 'save' 'y' To A '.mat' File
data = load("data.mat"); % 'load' To A Structure
y = data.y; % Retrieve 'y' From The 'data' Structure
figure
hold on
plot(y(1,:))
plot(y(7,:))
The original problem was likely that plot cannot plot structures, that ‘y’ originally was in this context, so it is necessary to recover the matrix from the ‘data.mat’ file structure first.
.
  2 个评论
Anthony Koning
Anthony Koning 2023-4-11
For line 5, using this code results in an error with the .y portion of the code, claiming "Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses." What would be causing this?
Star Strider
Star Strider 2023-4-11
I don’t have your ‘data.mat’ to work with so I created my own to test my code. I’m assuming that your ‘data.mat’ is similar to the one I created. If it isn’t, and since I have no idea what is in it, I can’t solve that problem.
Please run this from a script or your Command Window and then copy that result and paste it to a Comment here:
LD = load("data.mat")
That will at least tell me what is in the file. I also need to know what variable you want to retrieve from it and what you want to plot. Just now, none of that has been presented.

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