Trying to add a variable RowName based off for loop.

Hello, I am trying to create a table where each row name is the name of the file that I am manipulating. I was able to get it to work the first iteration, but after that im having trouble. I figured the way I had it would work, but am having trouble. Any help would be appreciated, thanks!

textfiles = dir('*.txt');
library = cell(1,length(textfiles));
matrix = zeros(50,7);
avgvec = ones(1,7);
avgmatrix = zeros(length(textfiles),7);
for ii = 1:length(textfiles)
    fid = fopen(textfiles(ii).name);
    library{ii} = readtable(textfiles(ii).name, 'Delimiter', '\t', 'ReadVariableNames', false, 'HeaderLines', 9);
    matrix = library{ii}(:,2:8).Variables;
    avgvec = mean(matrix);
    avgmatrix(ii,:) = avgvec;
    
    avgtablevec = array2table(avgvec, 'RowNames', {textfiles(ii).name}, 'VariableNames', {'q', 'V_ref', 'alpha', 'NormalForce', 'AxialForce', 'Moment', 'P'});
    averagetable(ii, :) = avgtablevec;
end

Answer 1

[Himanshu]

Hey Jacob,

MATLAB tables don't directly support dynamic row names assignment in the way you're attempting. Instead, you should create a table with all the data first and then assign the row names separately.

You can refer to the following code:

textfiles = dir('*.txt');
numFiles = length(textfiles);
avgmatrix = zeros(numFiles, 7);
rowNames = cell(numFiles, 1);

for ii = 1:numFiles
    % Read the file and extract the relevant data
    library = readtable(textfiles(ii).name, 'Delimiter', '\t', 'ReadVariableNames', false, 'HeaderLines', 9);
    matrix = library{:, 2:8};

    % Calculate the mean for each column
    avgvec = mean(matrix);
    avgmatrix(ii, :) = avgvec;
    
    % Store the filename for row naming
    rowNames{ii} = textfiles(ii).name;
end

% Create the table with the calculated averages
averagetable = array2table(avgmatrix, 'VariableNames', {'q', 'V_ref', 'alpha', 'NormalForce', 'AxialForce', 'Moment', 'P'});

% Assign the row names
averagetable.Properties.RowNames = rowNames;

% Display the table
disp(averagetable);

You may also go through this Matlab answer thread, which is a discussion on the same issue:

https://in.mathworks.com/matlabcentral/answers/1976449-assign-name-row-to-table

Answer 2

[Stephen23]

You can certainly add rownames dynamically in a loop, but not by indexing one table into an existing table.

Nrow = 5;
Ncol = 7;
T = table('Size',[Nrow,Ncol], 'VariableTypes',repmat("double",1,Ncol));
for k = 1:Nrow
    T{k,:} = rand(1,Ncol);                % row values
    T.Properties.RowNames(k) = "MyRow"+k; % row name
end
display(T)

T = 5x7 table
               Var1        Var2        Var3       Var4       Var5        Var6       Var7  
              _______    ________    ________    _______    _______    ________    _______

    MyRow1    0.64754    0.034667     0.21142    0.64744    0.94951    0.044792    0.92204
    MyRow2    0.92099     0.93698     0.17448    0.44149    0.34022     0.64313    0.66402
    MyRow3    0.62632     0.66785     0.82359    0.51254    0.83964     0.89535    0.13099
    MyRow4    0.97673      0.7379     0.35095    0.73779    0.13757     0.49799    0.17754
    MyRow5     0.2926     0.22048    0.028628    0.92226    0.14278     0.78226    0.40858

Answer 3

[埃博拉酱]

Table is what you really need to pre-allocate, and you don't need other variables at all.

textfiles = dir('*.txt');
library = cell(1,length(textfiles));
averagetable=table;%Tables are what you really need to pre-assign
for ii = 1:length(textfiles)
	% fid = fopen(textfiles(ii).name);%This variable is not used at all, and you forgot to fclose the file you opened
	library{ii} = readtable(textfiles(ii).name, 'Delimiter', '\t', 'ReadVariableNames', false, 'HeaderLines', 9);

	%Tables should be indexed directly with row and column names
	averagetable{textfiles(ii).name, {'q', 'V_ref', 'alpha', 'NormalForce', 'AxialForce', 'Moment', 'P'}} = mean(library{ii}{:,2:8},1);
end