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

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Srinivasa Raghavan Raghuraman
评论： Srinivasa Raghavan Raghuraman 2021-1-22
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
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Stephen23
Stephen23 2021-1-21
"...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
Srinivasa Raghavan Raghuraman 2021-1-22
Thank you Mathieu NOE and Stephen Cobeldick. I can now keep each of my iteration data in a variable with indexing.

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回答（1 个）

Bob Thompson
Bob Thompson 2021-1-21
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.
  2 个评论
Stephen23
Stephen23 2021-1-21
编辑：Stephen23 2021-1-21
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
Srinivasa Raghavan Raghuraman 2021-1-22
Thank you Bob Thompson and Stephen Cobeldick for your time and help. The indexing method works very well for my problem.

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