reading data, loop and plot.

I'm trying to get the year and CO2 levels from a txt file, plot them on a x-y graph. I have a problem with my loop.The -99.99 values are bad statistics that I try to remove. My x and y are just one value, respectively. Shouldn't they be two arrays??

 filename = input('Please enter the file name: ');
 fid01 = fopen(filename,'r');
 for i = 1:15
    line = fgets(fid01);
 end
 for i = 16 : 66
    line = fgets(fid01);
    z = strread(line,'%s');
    year = str2num(z{1});
    for j = 2:13
        monthly_entry = str2num(z{j});
        if (monthly_entry == -99.99)
            monthly_entry = [ ];
        end
        x = year + 1/12;
        y = monthly_entry;
    end

 end

 plot(x,y);

Answer 1

[Walter Roberson]

No, they should be single values. You are writing over all of the variables each iteration of your "for j"

x = year + 1/2;

overwrites all of x, leaving x of whatever length "year" happens to be.

More typical would be to store into something indexed by your loop variables, such as

x(i, j) = year + 1/2;
y(i, j-1) = monthly_entry;

However, you set monthly_entry to [], which is length 0, for data that is bit-for-bit identical to whatever MATLAB happens to interpret -99.99 as being this time around, a match that would be rare but would occur by accident from time to time. (I already told you about this code being incorrect.) If that ever does happen, you would be unable to store the length-0 [] into the length-1 y(i,j-1)

Your handling of bad data is not well defined. I would suggest to you that your handling would be considerably better defined if you used NaN or 0 for those cases instead of trying to leave a hole in the data.

[Jovos]

I tried to use

 x(i,j)= year + 1/2;

But the x-axis still is one single value. By the way, how do I throw away i from 1 to 15?

[Walter Roberson]

 for i = 1:15
    line = fgets(fid01);
 end

already throws away lines 1 to 15.

[Walter Roberson]

You seem to be doing a lot of unnecessary work.

fmt = repmat('%f',1,14);
fid = fopen('CO2.txt','rt');
data = textscan(fid, fmt, 'HeaderLines', 15, 'CollectOutput', 1);
fclose(fid);

x = data{1}(:,1);
y = data{1}(:,2:end);
plot(x, y);
legend({'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec', 'Avg'});

[Jovos]

So now I have all the values, how could I arrange these values into a X array? SO that I can plot it?

 filename = input('Please enter the file name: ');
 fid01 = fopen(filename,'r');
 for i= 1:15
    line = fgets(fid01);
 end

 for i = 16:66
    line = fgets(fid01);
    z = strread(line,'%s');
    year = str2num(z{1});  
    for j = 2:13
        dat = str2num(z{j});
        if ( dat== -99.9900)
            dat = NaN;
        end      

    end

 end