reading data, loop and plot.

Question

Jovos 2016-2-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/269101-reading-data-loop-and-plot

编辑： Walter Roberson 2016-2-20

CO2.txt

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);

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Answer 1

Walter Roberson 2016-2-20

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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.

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Walter Roberson 2016-2-20

编辑：Walter Roberson 2016-2-20

在 MATLAB Online 中打开

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 2016-2-20

编辑：Jovos 2016-2-20

在 MATLAB Online 中打开

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