Graphing from txt file? - Homework

I am not sure what is wrong with the script:

So the data looks like this:

World population

YEAR BC/AD POPULATION

10000 BC 1000000

8000 BC 5000000

6500 BC 5000000

5000 BC 5000000

I need to use the first column (year) as the x axis (as negative numbers if BC and positive is AD).

I need the third column to be the y axis in log scale (I am having trouble with this part too).

My script so far:

[fid, msg] = fopen('hw12_2.txt','w');
if fid==-1
    fprintf(2,'FAILED TO OPEN FILE. %s\n', msg);
    return;
end

% FIRST LINE OF DATA
title_str= fgetl(fid);

% SECOND LINE HAS LABELS
aline=fgetl(fid);
[x_str, ystr]=strtok(aline);
y_str = ystr(7:end);

hold on

line1 = fgetl(fid);
line2 = fgetl(fid);
y = fid(:,3);
x = fid(:,1);
plot(x,y);

% USE LABELS FROM ABOVE USING FIRST AND SECOND LINE
xlabel(x_str);
ylabel(y_str);
title(title_str);

hold off

Answer 1

[Umair Nadeem]

I get it what you are trying to achieve. Here is the code I developed after a little modification of yours.

clear all;
clc;

[fid, msg] = fopen('hw12_2.txt','r');
if fid==-1
    fprintf(2,'FAILED TO OPEN FILE. %s\n', msg);
    return;
end

% FIRST LINE OF DATA
title_str= fgetl(fid);

% Initialize z and y axis arrays
xstr =[];
ystr =[];

aline = 1;

while aline ~= -1

      % SECOND LINE HAS LABELS
      aline=fgetl(fid);
      if (aline ~= -1)

          [x_str, y_str_temp] = strtok(aline);
          [Dec, y_str] = strtok(y_str_temp);
          x_str = str2double(x_str);
          y_str = str2double(y_str);

          % cmpr stores the result of comparison of both strings i.e. check
          % whether it is equal to BC or not
          cmpr = strcmp(Dec, 'BC');

          if (cmpr == 1)
              x_str = -1 * x_str;
          end

          xstr = [xstr x_str];
          ystr = [ystr y_str];

      end
  end

% Convert the y-axis in log scale

ystr = log10(ystr);

bar(xstr,ystr);

% USE LABELS FROM ABOVE USING FIRST AND SECOND LINE
xlabel('Year');
ylabel('Population');
title(title_str);

It works perfectly fine and just like the way you want it, but you have to take care of one thing that the text file must not have any empty lines between the line with actual text, otherwise the compiler would take that the file has ended and it will return a -1. It should be like this

YEAR BC/AD POPULATION
10000 BC 1000000
8000 BC 5000000
6500 BC 5000000
5000 BC 5000000

This way it will work absolutely fine. Hope it helps

[G A]

If you want the Y scale to be logarithmic (without transforming the data to log10), you can use:

set(gca,'YScale','log')

before plot, bar or hold on

[Umair Nadeem]

Ok now it would work with a file with alternate empty lines also :)

clear all;
  clc;

    [fid, msg] = fopen('hw12_2.txt','r');
    if fid==-1
        fprintf(2,'FAILED TO OPEN FILE. %s\n', msg);
        return;
    end

    % FIRST LINE OF DATA
    title_str = fgetl(fid);

    % Dump the result for an empty line
    dump = fgetl(fid);

    % SECOND LINE HAS LABELS
    line_2 = fgetl(fid);

    % Initialize z and y axis arrays
    xstr =[];
    ystr =[];

    aline = 1;

    while aline ~= -1

          % Dump the result for an empty line
          dump2 = fgetl(fid);

          % ALL DATA LINES
          aline=fgetl(fid);
          if (aline ~= -1)

              [x_str, y_str_temp] = strtok(aline);
              [Dec, y_str] = strtok(y_str_temp);
              x_str = str2double(x_str);
              y_str = str2double(y_str);

              % cmpr stores the result of comparison of both strings
               % i.e. check
              % whether it is equal to BC or not

              cmpr = strcmp(Dec, 'BC');

              if (cmpr == 1)
                  x_str = -1 * x_str;
              end

              xstr = [xstr x_str];
              ystr = [ystr y_str];

          end
      end

    % Convert the y-axis in log scale

    ystr = log10(ystr);

    bar(xstr,ystr);

    % USE LABELS FROM ABOVE USING FIRST AND SECOND LINE
    xlabel('Year');
    ylabel('Population');
    title(title_str);

It would work with this type of file with empty lines in between

World population

YEAR BC/AD POPULATION

10000 BC 1000000

8000 BC 5000000

6500 BC 5000000

5000 BC 5000000

[Nora]

This helped a bit. The data actually doesn't have spaces inbetween each line. And I am still having trouble with the graphing portion though.

[Image Analyst]

You forgot to post your data file. How can they properly write a program if they're just guessing (wrong apparently) at how your data is formatted? Use the paper clip icon and don't forget to click the "Attach File" button after you browsed to your file.

[Nora]

The data isn't showing on the graph. There is a blank graph with the script.

[fid, msg] = fopen('hw12_2.txt','r');
    if fid==-1
        fprintf(2,'FAILED TO OPEN FILE. %s\n', msg);
        return;
    end
    % FIRST LINE OF DATA
    title_str = fgetl(fid);
    % Dump the result for an empty line
    dump = fgetl(fid);
    % SECOND LINE HAS LABELS
    line_2 = fgetl(fid);
    % Initialize z and y axis arrays
    xstr =[];
    ystr =[];
    aline = 1;
    while aline ~= -1
          % Dump the result for an empty line
          dump2 = fgetl(fid);
          % ALL DATA LINES
          aline=fgetl(fid);
          if (aline ~= -1)
              [x_str, y_str_temp] = strtok(aline);
              [Dec, y_str] = strtok(y_str_temp);
              x_str = str2double(x_str);
              y_str = str2double(y_str);
              % cmpr stores the result of comparison of both strings
               % i.e. check
              % whether it is equal to BC or not
              cmpr = strcmp(Dec, 'BC');
              if (cmpr == 1)
                  x_str = -1 * x_str;
              end
              xstr = [xstr x_str];
              ystr = [ystr y_str];
          end
      end
    % Convert the y-axis in log scale
    ystr = log10(ystr);
    semilogy(ystr);
    % USE LABELS FROM ABOVE USING FIRST AND SECOND LINE
    xlabel('Year');
    ylabel('Population');
    title(title_str);

???

[Image Analyst]

Looks like hw12_2.txt somehow didn't get attached. Try again. Make sure you click the "Attach file" button after you click the "Choose file" button.

[Nora]

I found out the problem. Thank you!