Loop through csv file -- please help

%Hi! I am trying to step through a csv file to covert each video time into a frames. Ideally, I want to rewrite a new column in the csv column to be the converted frames. The video times are not equally incremented. The data is in a %csv file. frame = ([time in csv file]*Tframe)/Vtime where Tframe is total frames & Vtime is the total video time. Thanks!

%Video time to frames

%user entered data

Vtime = input('Length of video: '); %total length of video

Tframe = input('Total # of frames: '); %total number of frames

fid=fopen('test.csv', 'r')

k=length(fid);

while ~feof(fid)

k=k+1;

Z{k}=fgetl(fid);

frame = (Z{k}*Tframe)/Vtime;

end

fclose(fid)

x=[frame]

%The wrong values and the wrong number of values are being returned. Thanks for your help!

[Image Analyst]

What is in the CSV file? Individual frame times, or image data? Or both?

Answer 1

[Voss]

Note that fgetl returns a character vector, so multiplying that by Tframe isn't what you mean to do. You can try converting that character vector to a numeric value using str2double like this:

%Video time to frames 
%user entered data 
Vtime = input('Length of video: ');  %total length of video 
Tframe = input('Total # of frames: '); %total number of frames 
fid=fopen('test.csv', 'r');
k = 0;
while ~feof(fid) 
    k=k+1;
    Z(k)=str2double(fgetl(fid));
    frame(k) = (Z(k)*Tframe)/Vtime;
end
fclose(fid);
x=[frame]

This assumes that each line has one number signifying a time on it and nothing else.

In any case, it's probably better and easier to read the file using readmatrix or readcell (or xlsread or csvread if you have an older version of MATLAB), depending on what all is in the .csv file and what all you need out of it.

[Jenna Ceraso]

Thank you so much!!!!

[Image Analyst]

OK, since you say this worked, you probably shouldn't call the variable frame. When you call it frame, people will think of it as a 2-D color or gray scale image, which it's not - it's just a vector of single, scalar numbers. That's what confused me and why my answer didn't work for you. You should probably call the variable frameTimes or something more descriptive like that.

I don't know what x is or how you use it later but you don't need the brackets around frame, so assign it like this

x = frameTime;

And you don't need a for loop. You can do it vectorized like this

Z = readmatrix('test.csv');
fractionOfWayThrough = linspace(0, VTime, Tframe);
frameTime = Z * fractionOfWayThrough

[Voss]

@Jenna Ceraso You're welcome!

[Stephen23]

"it's probably better and easier.." and faster and a better use of your time "...to read the file using readmatrix"

Answer 2

[Image Analyst]

fid is the file handles so there is no reason to set k equal to it and have it be some kind of line counter.

Use readmatrix() or csvread() to read in the data from the CSV file, not fgetl(). You'll get the whole matrix at once and don't need to get it a line at a time. Your Z{k} would be a text string anyway, so that doesn't make sense.

[Jenna Ceraso]

Good to know. Thanks!