Problem with graphing different plots on the same graph within a ‘for’ loop.

Hi,

I just have a problem with graphing different plots on the same graph within a ‘for’ loop. I hope someone can be point me in the right direction.

I have a 2-D array, with discrete chunks of data in and amongst zeros. My data is the following:

A=

        0           0
        0           0
        0           0
        3           9
        4          10
        5          11
        6          12
        0           0
        0           0
        0           0
        0           0
        7         9.7
        8         9.8
        9         9.9
        0           0
        0      0

A chunk of data is defined as contiguous set of data, without interruptions of a [0 0] row. So in this example, the 1st chunk of data would be

        3           9
        4          10
        5          11
        6          12

And 2nd chunk is

        7        9.7
        8        9.8
        9        9.9

The first column is x and second column is y. I would like to plot y as a function of x (x is horizontal axis, y is vertical axis) I want to plot these data sets on the same graph as a scatter graph, and put a line of best fit through the points, whenever I come across a chunk of data. In this case, I will have 2 sets of points and 2 lines of best fit (because I have 2 chunks of data). I would also like to calculate the R-squared value

The code that I have so far is shown below:

     fh1 = figure;
         hold all;
        ah1 = gca;

    % plot graphs:
    for d = 1:max_number_zeros+num_rows
    if sequence_holder(d,1)==0
        continue;
    end
    c = d;
    while sequence_holder(c,1)~=0
        plot(ah1,sequence_holder(c,1),sequence_holder(c,num_cols),'*');
        %lsline;
        c =c+1;
        continue;
    end
    end

Sequence holder is the array with the data in it. I can only plot the first set of data, with no line of best fit. I tried lsline, but that didn't work.

Can anyone tell me how to

-plot both sets of graphs

-how to draw a line of best fit a get the regression coefficient?

Answer 1

[dpb]

For each group over the ranges,

scatter(x,y)       % where x,y are over the ranges, of course
if loopIndex==1, hold on, end  % add to the plot
b=polyfit(x,y,1);  % also as above...
yhat=polyval(b,[x(1) x(end)]);  % evaluate the fit at end points
plot([x(1) x(end)],yhat);  % plot the fitted line

Repeat the above for each set of indices in the groups...there are multiple other ways to attack such a problem; one is that can replace 0>>NaN and plot all the points at once; the NaN values will just be ignored. All will be one color for the data points that way which may (or may not) be desired effect.

[Harry]

Hi dbp,

Could you tell me how this code plots on the same graph within a for loop ?

How this code fits into my code above ?

Also what is the "loopIndex == 1, hold on, end" do ?

Sorry for my questions, but I'm a little new to matlab.

Thanks.

[dpb]

You include it within the loop wherein you've determined the sections and number thereof; each pass uses the indices of that subsection.

The if clause simply sets hold on after the first plot--once it's 'on' there's no point in doing it over and over. That's the "trick" to add additional information on the same axes object; the first plot is created with the defaul condition of hold off; then 'on' retains that data and some other state variables for the express purpose of adding to that plot. See

doc hold  % for details