read multiple .csv files in 'for loop', extract and write data to .txt

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Doug Leaffer
Doug Leaffer 2022-10-4
评论： Benjamin Thompson 2022-10-5
I am having some difficulties reading multiple .csv files in a 'for loop', extracting and writing data to .txt My code is below. There are ~150 .csv files in a single folder. I want to extract selected rows/columns from each file (the same row and column #'s in every file) then write the extracted data to .txt file with ~150 readings in 3 columns for processing. Any help or advice is appreciated. My code below only extracts one data point.
% Read multiple .csv noise files (LD831) LCeq-LAeq values and 1/3-OB
files = dir('*.csv');
% Then iterate over the files struct to read each file.
for i=1:length(files)
%data = readmatrix(files(i).name); % or csvread(files(i).name)
% process data
data = xlsread(files(i).name, 'B81:AK82'); % read noise file 1/3-OB data
LC_LA = xlsread(files(i).name, 'B63:B63'); % LCeq - LAeq reading
% Extract dB values for VLFN and LFN
VLFN = 10*log10(10.^(data(2,1)/10)+10.^(data(2,2)/10)+10.^(data(2,3)/10)+10.^(data(2,4)/10)+10.^(data(2,5)/10)+10.^(data(2,6)/10));
LFN = 10*log10(10.^(data(2,7)/10)+10.^(data(2,8)/10)+10.^(data(2,9)/10)+10.^(data(2,10)/10)+10.^(data(2,11)/10)+10.^(data(2,12)/10)+10.^(data(2,13)/10)+10.^(data(2,14)/10));
%MFN =
%HFN =
writematrix(LC_LA,'deltaC_Rox.txt'); % save to txt file
% need to add VLFN, LFN values to .txt file ...HOW?
end
  2 个评论
Stephen23
Stephen23 2022-10-4
You can set the WRITEMATRIX option 'WriteMode' to 'append' and then carefully specify the range you wish to write to each time:
https://www.mathworks.com/help/matlab/ref/writematrix.html#namevaluepairarguments
But most likely it would be simpler to collect the data into one array within the loop and save it once after the loop.
Doug Leaffer
Doug Leaffer 2022-10-4
adding 'WriteMode', 'append' to the code di not result in a compilation vector of additional values culled from each .csv file

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回答（2 个）

Benjamin Thompson
Benjamin Thompson 2022-10-4
So building on Stephen's comment. You may also get better results using readmatrix or readtable than xlsread.
% Read multiple .csv noise files (LD831) LCeq-LAeq values and 1/3-OB
files = dir('*.csv');
outputmatrix = zeros(length(files),3) % Not sure how many columns here but you said three
% Then iterate over the files struct to read each file.
for i=1:length(files)
%data = readmatrix(files(i).name); % or csvread(files(i).name)
% process data
data = xlsread(files(i).name, 'B81:AK82'); % read noise file 1/3-OB data
LC_LA = xlsread(files(i).name, 'B63:B63'); % LCeq - LAeq reading
% Extract dB values for VLFN and LFN
VLFN = 10*log10(10.^(data(2,1)/10)+10.^(data(2,2)/10)+10.^(data(2,3)/10)+10.^(data(2,4)/10)+10.^(data(2,5)/10)+10.^(data(2,6)/10));
LFN = 10*log10(10.^(data(2,7)/10)+10.^(data(2,8)/10)+10.^(data(2,9)/10)+10.^(data(2,10)/10)+10.^(data(2,11)/10)+10.^(data(2,12)/10)+10.^(data(2,13)/10)+10.^(data(2,14)/10));
%MFN =
%HFN =
outputmatrix(i,:) = [data LC_LA];
% need to add VLFN, LFN values to .txt file ...HOW?
end
writematrix(outputmatrix,'deltaC_Rox.txt'); % save to txt file
  2 个评论
Doug Leaffer
Doug Leaffer 2022-10-4
Thank you for you comments Ben. This only resulted in more errors. Also - readtable and readmatrix did not work
Benjamin Thompson
Benjamin Thompson 2022-10-5
Without having all the data files I was only guessing but glad you ended up with a good result anyway.

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Doug Leaffer
Doug Leaffer 2022-10-5
The code below seems to work for my needs. Thanks for your input Steven and Benjamin.
%% READ CSV Noise Files LCeq-LAeq and VLFN, LFN, MFN, HFN
% Get a list of all txt files in the current folder, or subfolders of it.
fds = fileDatastore('*.csv', 'ReadFcn', @importdata)
fullFileNames = fds.Files
numFiles = length(fullFileNames)
% Loop over all files reading them in and plotting them.
for k = 1 : numFiles
fprintf('Now reading file %s\n', fullFileNames{k});
data = xlsread(fullFileNames{k}, 'B81:AK82'); % read noise file data
LC_LA = xlsread(fullFileNames{k}, 'B63:B63'); % LCeq - LAeq reading
% Extract dB values for VLFN and LFN
VLFN = 10*log10(10.^(data(2,1)/10)+10.^(data(2,2)/10)+10.^(data(2,3)/10)+10.^(data(2,4)/10)+10.^(data(2,5)/10)+10.^(data(2,6)/10));
LFN = 10*log10(10.^(data(2,7)/10)+10.^(data(2,8)/10)+10.^(data(2,9)/10)+10.^(data(2,10)/10)+10.^(data(2,11)/10)+10.^(data(2,12)/10)+10.^(data(2,13)/10)+10.^(data(2,14)/10));
%MFN =
%HFN =
%
writematrix(LC_LA, 'delta_C_Rox.txt', 'WriteMode', 'append'); % save to txt file
writematrix(VLFN, 'VLFN_Rox.txt', 'WriteMode', 'append');
writematrix(LFN, 'LFN_Rox.txt', 'WriteMode', 'append');
%vwritematrix(MFN, 'LFN_Rox.txt', 'WriteMode', 'append');
%vwritematrix(HFN, 'LFN_Rox.txt', 'WriteMode', 'append');
%
end
vlfn = readmatrix('VLFN_Rox.txt');
lfn = readmatrix('LFN_Rox.txt');
%mfn = readmatrix('MFN_Rox.txt');
%hfn = readmatrix('HFN_Rox.txt');
deltaC = readmatrix('delta_C_Rox.txt');
%
T = table(deltaC, vlfn, lfn); %ADD mfn, hfn);

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