How to use writetable in a for loop

Hi everyone,

I want to write a script that, for all files in my folder, selects a specific value out of a table and puts them together in one new table. I am using a for loop including the writetable command, but it creates a new file containing only the value of the last iteration. What am I doing wrong?

volumeTable = dir('*properties_aparc.mat') %% here I select the files I need out of my folder

for k = 1:length(volumeTable);

baseFilename = volumeTable(k).name;

fullFilename = fullfile(volumeTable(k).folder,baseFilename);

load(fullFilename);

T = regionPropertiesTable(31,4) %% Select row 31, column 4 from the regionPropertiesTable

writetable(T)

end

When I use regionPropertiesTable(x,y) outside of this code, it gives me a 1x1 table. I want to add the 1x1 tables of all my participants together into one file (.txt is fine).

Thanks in advance for your time! I am relatively new to MatLab.

Answer 1

[VBBV]

T{k} = regionPropertiesTable(31,4)

Use a cell array for all participants. Later use

writetable(T)

Outside of loop

[Daisy]

Hi VBBV,

Thank you for your fast reply! If I add T{k} I get the following error:

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not supported. Always specify a row subscript and a variable subscript, as in t(rows, vars).

Any idea how to get around this error?

Thanks again!

[VBBV]

Ok. Try with only

writetable(T,'filename.txt','WriteMode','Append')

Ignore the previous line

[Daisy]

This one gives me the error 'Invalid parameter name: WriteMode'

[Daisy]

Hi VBBV, I want to thank you again for your help, I solved my issue :)

As you suggested, I created a cell array and used the writetable command including 'WriteMode' and 'Append', which now creates a csv file with the values I need from the tables in one column. For others struggling like me, here is my code:

volumeTable = dir('*properties_aparc.mat')

for k = 1:length(volumeTable)

baseFilename = volumeTable(k).name;

fullFilename = fullfile(volumeTable(k).folder,baseFilename);

fprintf(1,'Now reading %s\n',fullFilename)

load(fullFilename);

T = regionPropertiesTable(31,4); %% takes ROI volume out of big table and creates a 1x1 table

Volumes{k} = T; %% puts all 1x1 tables in a cell array

writetable(Volumes{k}, 'VolumesTest.csv','WriteMode','Append') %%puts all ROI volumes in 1 column in a .csv file

end