Why do I get: Error using sum Invalid data type. First argument must be numeric or logical?

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lil brain 2023-3-14

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评论： lil brain 2023-3-16

Hi,

I have a cell array called "pre_data" with 1 column and 27 rows. Each element in the column contains a cell with 21 colums and a varying number of rows.

I want to scan the columns in the cells of pre_data. For each seperate column, if there are values in a column that are above 3 standard deviations of that column, then I want the row cointaining that value to be removed.

For that I have written the following piece of code:

pre_data_clean = cell(size(pre_data));
% iterate over each cell in pre_data
for i = 1:length(pre_data)
    data_pre = pre_data{i}; % get the data in the current cell
    means_pre = cellfun(@mean, data_pre, 'UniformOutput', false); % calculate the means of each column
    stds_pre = cellfun(@std, data_pre, 'UniformOutput', false); % calculate the standard deviations of each column
    % remove values that are above 3 standard deviations from the mean
    for j = 1:size(data_pre{1}, 2) % iterate over each column
        for k = 1:length(data_pre) % iterate over each row in each cell
            data_pre{k}(:, j) = data_pre{k}(:, j) .* (abs(data_pre{k}(:, j) - means_pre{k}(j)) <= 3*stds_pre{k}(j));
        end
    end
    pre_data_clean{i} = data_pre; % save the cleaned data to pre_data_clean
end

The code seems to me like it works. But when I apply the code for other cell arrays that I have (balls_data, between_data, baskets_data or post_data), similar to "pre_data", then I continue to get error messages like this:

Error using sum

Invalid data type. First argument must be numeric or logical.

Error in mean (line 127)

y = sum(x, dim, flag) ./ mysize(x,dim);

Is this because the cell arrays have empty cells? If so, how can I fix this code?

Thank you!

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回答（1 个）

Walter Roberson 2023-3-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1928820-why-do-i-get-error-using-sum-invalid-data-type-first-argument-must-be-numeric-or-logical#answer_1193130

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You generally have cell arrays that contain cell arrays. However, in some places some of the entries are not cell arrays and are instead [] which is an empty double array.

Example fix:

baskets_data(cellfun(@isempty,baskets_data)) = {{}};

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Walter Roberson 2023-3-16

在 MATLAB Online 中打开

if isempty(data_balls)
  balls_data_clean{i} = data_balls;
  continue;
end

lil brain 2023-3-16

Thank you!

I have one last question. I just tried editing the code by making it scan for values above 1 SD... but nothing is removed which I think is not what would happen. Is the code performing correctly because it seems odd to me that not one value is above 1 SD.

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