MATLAB: Appending a csv file with existing data already in another column

Question

The purpose of the script I am writing is to weigh a number of subjects and record their mass, and then using my script and an image of the subject record their area.

I am trying to figure out if there is a way to write to an existing csv file (which has a column of masses already) and append it on the/an empty column. When I try this with csvwrite it overwrites the entire file.

Using dlmwrite as shown takes the mass column, puts it all in column A and then appends the end of the mass data

dlmwrite('filepath',areas,'roffset',0,'coffset',0,'delimiter',',','-append');

writematrix does the same thing

writematrix(areas,'filepath','WriteMode','append');

Ideally I want the csv to look like this and add data to the first column as it goes through every picture in the folder as per my script

1 area1 mass1

2 area2 mass2

3 area3 mass3

…

100 area100 mass100

right now all I get is

1 mass1

2 mass2

3 mass3

…

49 mass49

50 area1

….

100 area50

Here is the full script for reference purposes

format long g
myFolder = 'youfilepath';
% Get a list of all files in the folder with the desired file name pattern.
filePattern = fullfile(myFolder, '*.jpg'); % Change to whatever pattern you need.
theFiles = dir(filePattern);
for k = 1 : length(theFiles) %goes through all files in the folder
    baseFileName = theFiles(k).name;
    fullFileName = fullfile(theFiles(k).folder, baseFileName);
    
    I = imread(fullFileName); %reads in image files
    J = imcrop(I,[375,100,3800,2900]); %crop to subregion of 12 grid
    
    
    %BW = im2bw(J,0.375); %this is automatic threshold
    %BW2 = imcomplement(BW);
    %BW3 = imfill(BW2,'holes');
    
    imgcell=cell(1,12);
    p = 1;
    x = 950;
    for i = 1:3 %iterates through 3 rows
        y = 965*(i-1);
        for j = 1:4 %iteraties through the 4 columns
            imgcell{p} = imcrop(J,[x*(j-1),y,950,965]); %crops each grid cell
            p = p + 1;
        end
    end
    
   BW = cell(1,12); %preallocating cell arrays
   stats = cell(1,12);
    for i =1:12
        BW{i} = imgcell{i}(:,:,1)<95; %thresholding each gridded image
        BW{i} = imfill(BW{i},4,'holes'); %fills holes (very useful)
        stats{i} = regionprops(BW{i},'area'); %collecting pixel area
    end
    
    areas = zeros(1,12);
    for i = 1:12
        areas(i) = stats{i}.Area; %takes area field from stats cell array/structure and puts it into (more familiar) matrix form
    end
    
    cutoff = 2e-5; %cutoff area for a brand
    scale = 2.620670848e-8; %scale in m^2/pixel
    areas = areas*scale; %scaling pixel counts
    areas(areas<cutoff) = []; %taking out any values that dont meet the cutoff
    areas = transpose(areas); %1x12 isnt as nice as 12x1 in a csv
    
    writematrix(areas,'filepath\myfile.csv','WriteMode','append');
end

Answer 1

Hi Mahdi,

In my opinion, you can read the data first, modify it and then save the data back to the file.

Assuming you have csv file named testfile.csv (having column for masses already):

masses = [1,2,3,4];
masses = masses';
writematrix(masses,'testfile.csv');
% Assuming you have file as above 
M = csvread('testfile.csv');
% creating the areas column
areas = [10,20,30,40];
areas = areas';
% to make areas appear in first column
M = [areas M];
% save back to file
writematrix(M,'testfile.csv');

Regards,

Anmol Dhiman