How do I add rows to a table in a for loop?

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Alister
Alister am 23 Jan. 2023
Bearbeitet: Stephen23 am 25 Jan. 2023
I want to figure out how to take data from a list of tab-delimited .txt files of indeterminate length with formats like this:
Test Number Result
First test 1
First test 8
First test 3
First test 4
Test Number Result
Second test 201
Second test 208
Second test 203
Second test 204
And produce a table like this:
First 1 8 3 4
Second 201 208 203 204
filePattern = fullfile(myFolder, '*.txt'); % Change to whatever pattern you need.
theFiles = dir(filePattern);
for k = 1 : length(theFiles)
baseFileName = theFiles(k).name;
fullFileName = fullfile(theFiles(k).folder, baseFileName);
usableTable = readtable (fullFileName);
choppedTable = usableTable(:,["Test","Result"])
punyTable = choppedTable (1, "Test")
punyTable
SecondChopTable = choppedTable(:, "Result")
LongRow = rows2vars(SecondChopTable)
NewRow = [punyTable, LongRow]
NewRow.OriginalVariableNames = []
NewRow = vertcat(NewRow{i,:});
end
My problem is that, try as I might, I can't get NewRow to add rows onto the end of a table.
  3 Kommentare
Alister
Alister am 23 Jan. 2023
Bearbeitet: Stephen23 am 25 Jan. 2023
I have these files to work with (Sandbox1, Sandbox2, Sandbox3) and am trying to get the output seen in Result.txt.
This is my code, and it keeps producing the tables I want, but not in the order I want, and I don't know how to fix this.
addpath '\\myfiles.campus.edu\alister\Sandbox' %adds where the files are
myFolder = '\\myfiles.campus.edu\alister\Sandbox' % creates new folder
filePattern = fullfile(myFolder, '*.txt'); % Change to whatever pattern you need.
theFiles = dir(filePattern);
FileLength = length(theFiles)
for k = 1 : length(theFiles)
baseFileName = theFiles(k).name;
fullFileName = fullfile(theFiles(k).folder, baseFileName);
usableTable = readtable (fullFileName); %some kind of wonky BS that I don't understand. What I think is happening here is that this is
% somehow turning this into a real table function (whatever this means)
% that Matlab can then act upon.
choppedTable = usableTable(:,["Test","Result"])
punyTable = choppedTable (1, "Test")
punyTable
SecondChopTable = choppedTable(:, "Result")
LongRow = rows2vars(SecondChopTable)
NewRow = [punyTable, LongRow]
NewRow.OriginalVariableNames = [] %can use removevars in Matlab 2018+
for k = 1:H
T1 = table()
T1 = vertcat(T1,NewRow);
end
end
Stephen23
Stephen23 am 25 Jan. 2023
Bearbeitet: Stephen23 am 25 Jan. 2023
"addpath '\\myfiles.campus.edu\alister\Sandbox' %adds where the files are"
Do not add folders of data files to the MATLAB search path. The search path should be for code only.
"myFolder = '\\myfiles.campus.edu\alister\Sandbox' % creates new folder"
That line of code does not create any folder.
"some kind of wonky BS that I don't understand. What I think is happening here is that this is somehow turning this into a real table function (whatever this means)"
The READTABLE documentation explains what it does. The phrase "real table function" exists only on this thread.

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Antworten (2)

Star Strider
Star Strider am 23 Jan. 2023
The vertcat function needs to know what ‘NewRow’ is to be concatenated to.
Try something like this —
T1 = array2table(magic(5))
T1 = 5×5 table
Var1 Var2 Var3 Var4 Var5 ____ ____ ____ ____ ____ 17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9
for k = 1:3
NewRow = array2table(rand(1,5));
T1 = vertcat(T1,NewRow);
end
T1
T1 = 8×5 table
Var1 Var2 Var3 Var4 Var5 _______ _______ _______ ________ _______ 17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9 0.93963 0.769 0.84968 0.7547 0.33558 0.33767 0.33738 0.78089 0.54578 0.54718 0.65906 0.82833 0.59296 0.076004 0.46649
.
  4 Kommentare
Alister
Alister am 24 Jan. 2023
How would you do this if you had to grab files from a directory?
Star Strider
Star Strider am 24 Jan. 2023
I can’t demonstrate that easily here, however the general guidance is in: Import or Export a Sequence of Files
I would import all of them to a cell array in a loop, as I did here manually (since the directory structure here is a bit more complex than would usually be encountered) and then use the approach I used here to process the data to produce the desired final result.
.

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Stephen23
Stephen23 am 25 Jan. 2023
Bearbeitet: Stephen23 am 25 Jan. 2023
"... it keeps producing the tables I want, but not in the order I want, and I don't know how to fix this."
My guess (in lieu of your explanation) is that your filenames are numbered and you expect the file to be returned in numeric order. In that case you will need to sort the filenames alphanumerically. One way is to download my FEX submission NATSORTFILES, which was written to sort filenames into alphanumeric order:
In most cases it is very simple to include in your code:
P = '.'; % absolute/relative path to where the files are saved.
S = dir(fullfile(P,'*.txt'));
S = natsortfiles(S); % download here: https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort
for k = 1:numel(S)
F = fullfile(S(k).folder,S(k).name);
T = readtable(F);
S(k).data = T(:,["Test","Result"]);
end
T = vertcat(S.data);
[U,~,X] = unique(T.Test,'stable');
H = @(a) {num2cell(a.')};
C = splitapply(H,T.Result,X);
C = [U,vertcat(C{:})]
C = 3×24 cell array
{'First' } {[ 1]} {[ 8]} {[ 3]} {[ 4]} {[ 9]} {[ 2]} {[ 7]} {[ 6]} {[ 10]} {[ 18]} {[ 13]} {[ 14]} {[ 19]} {[ 12]} {[ 17]} {[ 16]} {[ 11]} {[ 21]} {[ 28]} {[ 23]} {[ 24]} {[ 29]} {[ 22]} {'Second'} {[201]} {[208]} {[203]} {[204]} {[209]} {[202]} {[207]} {[206]} {[2010]} {[2018]} {[2013]} {[2014]} {[2019]} {[2012]} {[2017]} {[2016]} {[2011]} {[2021]} {[2028]} {[2023]} {[2024]} {[2029]} {[2022]} {'third' } {[301]} {[308]} {[303]} {[304]} {[309]} {[302]} {[307]} {[306]} {[3010]} {[3018]} {[3013]} {[3014]} {[3019]} {[3012]} {[3017]} {[3016]} {[3011]} {[3021]} {[3028]} {[3023]} {[3024]} {[3029]} {[3022]}
T = cell2table(C)
T = 3×24 table
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 __________ ___ ___ ___ ___ ___ ___ ___ ___ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ {'First' } 1 8 3 4 9 2 7 6 10 18 13 14 19 12 17 16 11 21 28 23 24 29 22 {'Second'} 201 208 203 204 209 202 207 206 2010 2018 2013 2014 2019 2012 2017 2016 2011 2021 2028 2023 2024 2029 2022 {'third' } 301 308 303 304 309 302 307 306 3010 3018 3013 3014 3019 3012 3017 3016 3011 3021 3028 3023 3024 3029 3022
Your description is unclear about what data type you require the output to be, so I showed a few options for you.

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