Why does pcolor adds a flat lines during a data gap instead of white space?

I use pcolor command to make a color plot. The data has a some gaps (NaN values) in it where a white space is expected.

However, I get flat horizontal lines during that period. Any help appreciated. I tried both shading flat and shading interp, it shows same. However, I do see actual white space at certain instants. I could not figure out why! I attach an example for each case below. Both occurs in the same plot.

EDITS: Data Attached

h_fig = pcolor(T_,E_log,(double(FPDO))');
        % h_fig.EdgeColor = 'none';
        xlim([0,T_(end,1)]); ylim([-2.5,log10(30)]);
        colormap(jet);  shading interp;
        caxis([3,7]) % change caxis same as mar27_2017_omni_L_fesa_pile
        

Any help will be appreciated.

[Skye]

I faced a similar issue while working with pcolor for my assignment, where NaN values caused unexpected flat lines in the plot. One approach that helped me was ensuring the CData matrix was structured properly for MATLAB to interpret NaN as gaps. Additionally, I found that experimenting with different plotting functions, like imagesc, can sometimes handle NaN values better without those flat lines. If you’re looking for extra help, I highly recommend www.matlabassignmentexperts.com. They provided excellent guidance for my MATLAB project, and their support team is super responsive. You can reach them on WhatsApp at [phone] or email them at [e-mail].

Answer 1

[Voss]

load FPDO.mat
load E_log.mat
load T_.mat
T_ = T_lepi;

The problem is that T_ and E_log are not monotonic:

figure
subplot(2,1,1)
plot(T_,'.-')
ylabel('T\_')
subplot(2,1,2)
plot(E_log,'.-')
ylabel('E\_log')

So pcolor has to jump around and connect points across what would be the NaN gaps.

Sort the vectors and reorder the rows and columns of the matrix FPDO accordingly, pcolor with those reordered values, and you get the proper gaps where the NaNs are:

[T_sorted,Tidx] = sort(T_);
[E_log_sorted,Eidx] = sort(E_log);
FPDO_plot = FPDO(Tidx,Eidx);

figure
pcolor(T_sorted,E_log_sorted,FPDO_plot.');
axis tight
colormap(jet); shading interp;
clim([3,7])

Or reorder in the T dimension only:

[T_sorted,Tidx] = sort(T_);
FPDO_plot = FPDO(Tidx,:);

figure
pcolor(T_sorted,E_log,FPDO_plot.');
axis tight
colormap(jet); shading interp;
clim([3,7])

[megha]

@Voss amazing job! I would have never been able to figure this out! I appreciate your time and efforts. Thanks!

[Voss]

You're welcome!