How to sequentially import csv files, access, edit and save the data?

Hi friends,

I need to import .csv Data sequentially and read them as arrays, edit them and save them as seperate variables. I have tried to do the importing with "dir" with help of a for loop. But I do not know how to save the edited variables sequentially and because of this the for loop continuously replaces the previous variable with the data of the new one. I tried to plot the data out and I can get the plot figures of each instance of my loop, but the data is that of the last iteration.

%% Read The processes 1 to l

% Specify the folder

myFolder1 = 'C:\Users\';

% Get a list of all files in the folder with the desired file name pattern.

filePattern1 = fullfile(myFolder1, '*.csv'); % Format/ pattern

theFiles1 = dir(filePattern1);

for l = 1 :1: length(theFiles1)

baseFileName1 = theFiles1(l).name;

fullFileName1 = fullfile(theFiles1(l).folder, baseFileName1);

fprintf(1, 'Now reading %s\n', fullFileName1);

data_raw_P = readtable(fullFileName1);

%% % Now the csv is read as a table and saved in the variable data_raw_P. This causes the loop to replace the data read from the previous instance with the data from the latest instance. Is there any way to save as data_raw_P1, data_raw_P2, data_raw_P3 and so on? I need to use these data in the calculation and plotting part too.

%

% %% calculations

% %% figure,

figure,

%%%Since the graphs are not going to be replace with every iteration, my script generates the graphs for every step but I don't have any workspace variables to show for it!!!

end

[Mathieu NOE]

hello

you should index your output to keep every iteration in the workspace

data_raw_P{i} = readtable(fullFileName1);

[Stephen23]

"...I don't have any workspace variables to show for it"

Use indexing to store them in a variable, exactly like the MATLAB documentation shows:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

[Srinivasa Raghavan Raghuraman]

Thank you Mathieu NOE and Stephen Cobeldick. I can now keep each of my iteration data in a variable with indexing.

Answer 1

[Bob Thompson]

To save the results of a command each time you go through the loop you need to index the output. I recommend just adding a structure field to your existing files structure for the data.

%% Read The processes 1 to l
% Specify the folder 
myFolder1 = 'C:\Users\';
% Get a list of all files in the folder with the desired file name pattern.
filePattern1 = fullfile(myFolder1, '*.csv'); % Format/ pattern 
theFiles1 = dir(filePattern1);
for l = 1 :1: length(theFiles1)
    baseFileName1 = theFiles1(i).name;
    fullFileName1 = fullfile(theFiles1(i).folder, baseFileName1);
    fprintf(1, 'Now reading %s\n', fullFileName1);
    [theFiles1(i).Data] = readtable(fullFileName1); 

I haven't tested that bit of code, as I dont' have your files. There might be some issues with the exact syntax, it's been a while since I've last made a structure, but it should get you in the right direction.

[Stephen23]

Using the same structure returned by dir is a simple and efficient solution. A few remarks:

• The square brackets are not required if allocating one array:

theFiles1(i).Data = ...

• The end is missing at the end of the for loop.
• The for loop uses l as the iterator, but inside the loop the code uses i as an index. This will cause an indexing error as i is otherwise undefined and so refers to the imaginary constant.

[Srinivasa Raghavan Raghuraman]

Thank you Bob Thompson and Stephen Cobeldick for your time and help. The indexing method works very well for my problem.