Extracting 'y' values from plot over an iterating loop

Hello All,

I am trying to extract y values from a plot in matlab. I have used the below code snippet. However, as I have a for-loop iterating (which is needed as I need those values), it keeps giving me an "error using interp1- X must be a vector of numeric coordinates". Any suggestions? Thanks!

figure(107);
for i = 1:25
        p1 = loglog(Frequency{i,:},Svg{i,:});        %%%%,'Color',map(i,:)); %%%
        LineH = get(gca,'children');
        freq=get(LineH,'XData');
        psd=get(LineH,'YData');
        freq_10 = 10;   % the x value for which I need the y value
        svg_10{i} = interp1(freq,psd,freq_10);
        hold on;
end

[Adam]

Have you stepped into the code with the debugger and a breakpoint to see what freq and psd are?

[Kash022]

Hi, Yes..sorry forgot to mentioned that freq and psd are 25x800 matrices. So my code essentially should select the psd value for each of the 25 runs from the psd and freq matrices which are each 1x800

[Elias Gule]

Try using

LineH = findobj(gca,'Type','line'); % All line objects of the current axes
LineH = LineH(i); % Handle for the current line object

[Adam]

If you want to extract things from a line graphics object though by far your best option is to just retain the line handle when you plot it. It is more efficient than having to search the scene for it afterwards.

Answer 1

[Adam]

Well if freq and psd are 2d matrices then

interp1(freq,psd,freq_10);

is not going to work because interp1 expects vector inputs not a matrix. You should be able to use interp2 on it though, just making sure that in the second dimension your input and output grids are the same so that you don't interpolate in that direction.

Maybe you just meant to use this instead?

svg_10{i} = interp1(freq(i,:),psd(i,:),freq_10);

[Kash022]

Hello@Adam: yes, I tried this exactly...but to no use

[Adam]

In what sense? Do you get the same error message? Your inputs to interp1 should at least be vectors in this case.