How to split data into two matrices

Question

Lucas 2014-11-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/161190-how-to-split-data-into-two-matrices

编辑： Star Strider 2014-11-7

I am doing some analysis for my Honor's Thesis and am having some problems pre-processing of the data. The data is in a 4x147000 matrix. Row one is the time, two and three are my signals of interest, and the fourth is the stimulus - the condition I want to split the data up by. Due to imperfect data, not all of the events are the same length, so I need to take chunks of data either 490 or 990 columns long depending on the value of the fourth row. For example, I want to take the first 490 columns whose fourth row equals 0 and put into a new matrix "datanostim." Then I want to scan the matrix until the fourth row changes to 255, and take the first 990 columns whose fourth row equals 255 and add to a new matrix "datastim." This then repeats, so the next 490 columns whose fourth row is 0 is added to the datanostim matrix, the next 990 columns whose fourth row is 255 added to the datastim matrix, and so on.

Here is my attempt, but I would love to see other methods as well, as mine gives me the following: "Error: Function definitions are not permitted in this context."

function [datastim, datanostim] = datacutoff(data, stim, nostim)
%UNTITLED Summary of this function goes here
%   data = data as matrix, fourth row as stim 0 or 255
%   stim = length of stimulus
%   nostim = length without stimulus
datastim = [];
datanostim = [];
i = 1;
    if data(4,i) ~= data(4,i+1)
        i = i+1;
        else if data(4,i:i+nostim) == 0
            horzcat (data(:,i:i+nostim), datanostim);
            i = i+nostim;
            end
    end
    if data(4,i) ~= data (4,i+1)
        i = i+1;
        else if data(4,i:i+stim) == 255
            horzcat (data(:,i:i+stim), datastim);
            i = i+stim;
            end
    end
end

Thanks!

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Answer 1

Star Strider 2014-11-3

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/161190-how-to-split-data-into-two-matrices#answer_157601

"Error: Function definitions are not permitted in this context."

To solve that, you need to save your ‘datacutoff’ function to a separate .m-file ‘datacutoff.m’ in your MATLAB search path. Then you should be able to use it.

Then run it.

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Star Strider 2014-11-5

编辑：Star Strider 2014-11-5

在 MATLAB Online 中打开

Apologise for the late reply. A section of your data would help to verify this, but I believe I see part of the problem.

See if this works:

    Row4 = reshape(repmat([0 255], 10, 3), 1, []);  % Create Data
    data = [randi(10, 3, 60); Row4];                % Create Data
    chg = diff([1 data(4,:)]);       % Vector Of Changes From [0 255 0 255]
    stimidx = find(chg > 0);         % Start Of ‘255’ Segments
    nstmidx = find(chg < 0);         % Start Of ‘0’ Segments
    stimrng = 6;
    nstmrng = 7;
    datastim = [];
    datanostim = [];
    for k1 = 1:length(stimidx)
        datastim = [datastim data(:,stimidx(k1):stimidx(k1)+stimrng+1)];
    end
    for k1 = 1:length(nstmidx)
        datanostim = [datanostim data(:,nstmidx(k1):stimidx(k1)+nstmrng+1)];
    end

It seems to work as you want it to work with my test code, but I will leave it to you to make that determination. My ‘stimrng’ and ‘nstmrng’ variables are the lengths of the segments you will want to save, I believe 990 and 490 respectively. I kept them in the ranges of my simulated data to be sure they worked.

Lucas 2014-11-7

I'm glad because there is slight problem. When I run it at lengths of 490 for nostim and 990 for stim, the trial lengths aren't consistent. For example, the datanostim out put is a 4X48216, which means that out of 98 trials each is 492 bins. The problem also occurs for the datastim.

Star Strider 2014-11-7

编辑：Star Strider 2014-11-7

在 MATLAB Online 中打开

Delete the +1 at the end of the ‘datastim’ and ‘nodatastim’ assignments in the loops. If you’re still having problems, convert them to -1. (It wasn’t clear to me where you were counting from.)

Also, I just picked up a typo I didn’t see before. Change the ‘datanostim’ assignment to:

datanostim = [datanostim data(:,nostimind(k1):nostimind(k1)+nostimlen+1)];

changing the +1 as appropriate to get the addressing correct.

To avoid the problem with the index ranges exceeding the ‘data’ column size, you could put as the first statements in both for loops:

if (stimind(k1)+stimlen > length(data,2))
    return
end

and:

if (nostimind(k1)+nostimlen > length(data,2))
    return
end

respectively, and include the appropriate +1 or other indexing corrections there as well. That will test to be sure you’re not over-reading ‘data’, and if either one is true it will immediately return to the calling script rather than throwing the error. The ‘1:98’ limitation will not be necessary with these if blocks. If you’re happy with the ‘1:98’ limitation, keep them as they are now.

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