Find slope across columns of cell

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Carver Nabb 2019-1-4

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https://ww2.mathworks.cn/matlabcentral/answers/438337-find-slope-across-columns-of-cell

评论： Bob Thompson 2019-1-7

I have a 220x4 cell (a) consisting of numerical data and would like to find the (linear) slope across the four values in row one, then the four values in row two, and so on, so that I would end up with 220 different slopes that I could then save. Thanks in advance!

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Bob Thompson 2019-1-4

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https://ww2.mathworks.cn/matlabcentral/answers/438337-find-slope-across-columns-of-cell#answer_355079

How are you organizing the data into ordered pairs? I'm assuming that by 'numerical data' you mean you have cells that contain individual doubles.

data = cell2mat(a);
for i = 1:size(a,1)
    slope(i) = polyfit(x_vals,data(i,:),1);
end

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Carver Nabb 2019-1-7

This worked great, Bob, thank you. However, now that I have NaN values, the polyfit function returns only NaN for P and S when the row contains a NaN value. Is there a way to ignore the NaNs?

Bob Thompson 2019-1-7

for i = 1:size(a,1);
    pairs = [];
    pairs(:,1) = counter;
    pairs(:,2) = data(i,:);
    pairs = pairs(~isnan(pairs(:,2),:);
    slope(i) = polyfit(pairs(:,1),pairs(:,2),1);
end

This might not quite do it, the logic indexing to remove NaNs might be slightly off, but it should get you going at least.

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