Looping through columns to make subplots - matlab

Question

I have an spectral absorbance matrix in xls format which has column 1 as wavelength, and columns 2:3 as the associated absorbance spectra for particles from depth1 in water column. 2:3 are duplicates so they have to be plotted together. Next i have columns 4:5 as once again duplicate absorbance spectra for particles from depth2 in water column. Then data for depth3, depth4 etc. The matrix is 1001 rows by 13 columns.
I would like have 3 subplots (depth1, depth2 and depth3) in one figure with each subplot holding the 2 duplicate spectra of each depth.
I tried to follow the excellent responses to this question but this gives me one line per subplot but i want to plot two lines (duplicate spectra). So I did the following and it works but I can only get 3 subplots:
[num,txt,raw]=xlsread('ANACONDAS2010-ST1.xls');
legendCell=cellstr(txt);
figure
subplot(3,1,1)
plot(num(:,1), num(:,2:3),'r');grid on; box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(2:3)),legend boxoff
subplot(3,1,2)
plot(num(:,1), num(:,4:5),'b');grid on; box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(4:5)), legend boxoff
subplot(3,1,3)
plot(num(:,1), num(:,6:7),'g');grid on; box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(6:7)), legend boxoff
title('STATION 1','fontweight','bold','fontsize',16);
But as you can see this gives me only 1 figure with 3 subplots and the rest od the depths (d4, d5, d6) remain unplotted as i havent been able to specifiy them,
Because my script is long and cumbersome I would have liked to run this through a loop but I couldn't figure out how to do it in spite of battling with the code provided in the 2nd answer which I kind of understood unlike the first one.

Answer 1

Updated answer
Inserted version V2 of the code
Version V2 of the code allows displaying unlimited pairs of data, also it is even simpler than V1.
% Generation of example data
num=1:33;
number_of_data_colums=14;
num=[num' rand(length(num),number_of_data_colums)];
% Generation of legend string
for i=1:number_of_data_colums
legendCell{i}=['Absor. ' num2str(i)];
end
% Get the size of data to be plotted (columns from 2 to ...)
[r,c]=size(num);
n_data=floor((c-1)/2);
% Define the number of data to be plotted in each subplt
data_x_plot=2;
% Consistency check: if the number of column data is not even generate an
% error message and exit
if(n_data*2 ~= (c-1))
error('Number of data columns is not even')
else
% Define the number of subplot of each figure
n_sub_plot=3;
% Subplot and figure counters
s_plot_cnt=1;
fig_cnt=1;
% Create the first figure
figure
% External loop on figures
for i=2:2:n_data*2
% If three subplot have been added to a figure, open a new figure
if(s_plot_cnt == 4)
% The Title is assigne to the first subplot of each figure
title(ax(fig_cnt,1),['STATION ' num2str(fig_cnt)],'fontweight','bold','fontsize',16);
s_plot_cnt=1;
fig_cnt=fig_cnt+1;
figure
end
ax(fig_cnt,s_plot_cnt)=subplot(n_sub_plot,1,s_plot_cnt);
% The indices of columns to be plotted are computed automatically
plot(num(:,1), num(:,i:i+1));
grid on;
box on;
xlabel('Wavelength')
ylabel('Absorbance')
% add legend
legend(legendCell(i-1:i),-1)
% Increment subplot's counter
s_plot_cnt=s_plot_cnt+1;
% legend boxoff
end
end
% Add the last title
title(ax(fig_cnt,1),['STATION ' num2str(fig_cnt)],'fontweight','bold','fontsize',16);
Previous answer and
Version V1 of the code
I'm not sure I've understood your question, nevertheless, if you have 6 pairs of data and you want 3 subplot, you need 2 figures.
I've modified your original script in order to automatically determine the number of figure you need, generate the subplots and plot 2 set of data in each of them.
Updated code - now with legends
% Generation of example data
num=1:33;
num=[num' rand(length(num),12)];
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% UPDATED CODE STARS HERE
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Generation of legend string
legendCell{1}='Wavel';
for i=2:13
legendCell{i}=['Absor. ' num2str(i)];
end
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% UPDATED CODE ENDS HERE
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Get the size of data to be plotted
[r,c]=size(num);
% Define the number of data to be plotted in each subplt
data_x_plot=2;
% Define the number of subplot of each figure
n_sub_plot=3;
% Evaluate the number of figures to be created
n_fig=(c-1)/(data_x_plot*n_sub_plot);
% Define the index of data columns
idx=[2:2:c-1];
idx=reshape(idx,n_sub_plot,data_x_plot)';
% External loop on figures
for i=1:n_fig
figure
% Internal loop on subplots
for j=1:n_sub_plot
% The subplot indices are computed automatically
ax(i,j)=subplot(n_sub_plot,1,j);
% The indices of columns to be plotted are computed automatically
plot(num(:,1), num(:,idx(i,j):idx(i,j)+1));
grid on;
box on;
xlabel('Wavelength')
ylabel('Absorbance')
% add legend
legend(legendCell(idx(i,j):idx(i,j)+1),-1)
% legend boxoff
end
% The Title is assigne to the first subplot of each figure
title(ax(i,1),['STATION ' num2str(i)],'fontweight','bold','fontsize',16);
end
Given a set of 12 columns of data, this is the output:
Updated graphs, with legends

Answer 2

Maybe you should use Hold to retain current plot when adding new plots.
So your code should be like this:
[num,txt,raw]=xlsread('ANACONDAS2010-ST1.xls');
legendCell=cellstr(txt);
figure
subplot(3,1,1)
plot(num(:,1), num(:,2),'r');grid on;
hold on;
plot(num(:,1), num(:,3),'m');
box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(2:3)),legend boxoff
subplot(3,1,2)
plot(num(:,1), num(:,4),'b');
hold on;
plot(num(:,1), num(:,5),'c');
grid on; box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(4:5)), legend boxoff
subplot(3,1,3)
plot(num(:,1), num(:,6),'g');
hold on;
plot(num(:,1), num(:,7),'k');
grid on; box on; xlabel('Wavelength'), ylabel('Absorbance'),legend(legendCell(6:7)), legend boxoff
title('STATION 1','fontweight','bold','fontsize',16);