delete data of csv file

i have created a code such that data is appended to csv file every time the loop runs

but when i run the program again the new data is added with the old one

but i want to clear out the data in then csvfile before hand

what command do i use

delete('xyz.csv') deletes the whole file

[Merve Buyukbas]

I think this link is useful.

https://www.mathworks.com/matlabcentral/answers/566724-appending-a-csv-file-with-existing-data-already-in-another-column

[SINDU GOKULAPATI]

i acctually dont want to append

i want to delete the existing data completely

[Merve Buyukbas]

But you shouldn't count on the main directory and instead use full paths everywhere in your script. This way the data can be located anywhere independently on where the code is.

[SINDU GOKULAPATI]

im sorry i dont know if im not explaning properly

i have a csv file with all numbers it self ,let that be just 3 cells in my csv with data 1,2,3

if i open csv file i can see those three cells only

now using code in matlab i want to erase those

so now when i open that csv file it should be empty

there is no .txt or sring data

hope my question is conveys right

Answer 1

[Walter Roberson]

fclose(fopen('xyz.csv', 'w'));

When you open a file for writing with 'w' access, the existing content is discarded.

Note: the POSIX standard library specifies truncate() and ftruncate() functions that would be a closer match. However, MATLAB does not implement either of those.

[SINDU GOKULAPATI]

thank you very much walter it worked

[SINDU GOKULAPATI]

hello walter

after using that particular code im not able to perform csvread operation so is there any alternative?

[Walter Roberson]

? The entire purpose of this code is to "clear out the data in then csvfile before hand" . After using it, the file is going to be empty (provided that you had write access to the file.)

[SINDU GOKULAPATI]

dlmwrite('on.csv',(matrix),'-append')
s=csvread('D:\sem6\PROJECT\on.csv',1,2);
fclose(fopen('D:\sem6\PROJECT\on.csv','w'));

this is the order of my code but its giving a dlmread error (but i havent used dlmread)

[Walter Roberson]

csvread() calls dlmread() with delimiter ','

You are writing to a file that is not necesarily in the same place as you are reading from, as your current directory is not necessarily D:\sem6\PROJECT

[SINDU GOKULAPATI]

hey walter i specified the directory but still giving error,

for context 
for i=1:n
    for j=1:n
        angle = transpose(rnorm{i})*rnorm{j};
        if  angle > cosd(20) && angle <= cosd(0)
            matrix = [i,j,angle];
            dlmwrite('D:\sem6\PROJECT\on.csv',(matrix),'-append')
        end
    end   
    k=0;
    s=dlmread('D:\sem6\PROJECT\on.csv',',',1,2);
    store= histcounts(s);          //need histogram for each point wrt to angle subjected to other points 
    fclose(fopen('D:\sem6\PROJECT\on.csv','w'));   //to rewite for every 'i'
end

ps: i have attachec csv file with 50 rnorm value (intended output is 50 histograms)