legend problem when plotting netcdf data

Question

Luh Putri Adnyani 2021-4-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/798617-legend-problem-when-plotting-netcdf-data

回答： Luh Putri Adnyani 2021-5-4

I want to plot netcdf file (.nc) and the problem is in the legend as shown in picture below.

In the picture above, the legend should be in green line as well, however the result is still in red color line.

Here is my script:

x1=ncread('roms_his.nc','x_rho');
time1=ncread('roms_his.nc','ocean_time');
b1=ncread('roms_his.nc','bath');
bed=30-ncread('roms_his.nc','bath');
plot(x1,(squeeze(bed(:,1,1))),'red','LineWidth',2);
hold on 
plot(x1,(squeeze(bed(:,1,19))),'green','LineWidth',2);
hold off
xlabel('Length Distance, [m]')
ylabel('Bed elevation, [m]')
title ('Bed elevation along length distance after 75days (morpholofical factor=200)')
xlim([0 1200])
ylim([-1.3 1.1])
legend('initial(red)','morphfac=200(green)','Location','southwest','NumColumns',3)

I also try to change the legend setting, but the result is shown in picture below.

Can you help me to tackle this issue?

Thanks before.

Regards,

Luh

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Answer 1

DGM 2021-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/798617-legend-problem-when-plotting-netcdf-data#answer_672417

It's usually better to give legend the handles associated with the plots:

h1=plot(x,thing1,'b'); hold on;
h2=plot(x,thing2,'r');
legend([h1,h2],{'Thing 1','Thing 2'},'location','southwest')

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DGM 2021-4-11

编辑：DGM 2021-4-11

I didn't expect that. The problem appears to be that you're plotting multiple series with each plot command,(though the code doesn't look like it would be possible). At any rate, if you're getting that error, both h1 and h2 are column vectors of handles themselves. So doing [h1,h2] makes a 2D array of handles, which legend() doesn't know what to do with. It only accepts a vector of handles.

To resolve this, you can try concatenating them along the other dimension [h1;h2], but I have a feeling that you might not get what you want. You're specifying a legend with only two strings, but apparently you have more than two data series being plotted. Regardless, the end goal is to figure out which handles go with which series and just pass the handles you want.

It may help to see exactly how many objects are in h1 and h2 and try to figure out why they're not scalar.

h1
h2

FWIW, you can also do it like this:

plot(x1,start,'r','displayname','start');hold on ;
plot(x1,day75,'b','displayname','day75');
legend('location','southwest')

but you'll probably wind up with more labels than you expect for the exact same reason.

DGM 2021-4-11

Oh. I'm sorry. I didn't notice that x1 wasn't a vector. I'm still not sure what x1 looks like in relation to the data series. Could you not just use x1(:,1)? Surely there's redundancy in x1 if the plots are coming out coincident. I'm inclined to doubt that you need all 62 columns.