How can I add a third axis to a plot

I made a figure using yyaxis to plot two different kinds of data on the same plot. I want to add a third timeseries with a y-axis unique from the first two. I found the plotyyy function but one of my axes has three unique lines and it looks like plotyyy only allows one set of data per axis. Is there a straightforward way to add a third axis to the plot I already have?

Thank you in advance!

f4=figure(4)
box on
 
yyaxis left
hold on 
plot(MX,pkdosat_ns_1d,'-','color',[.4 .6 .6],'linewidth',2)
plot(MX,DO3_1d,'-','color','b','linewidth',2)  %[.4 .4 .4]
plot(MX,poDO4_1d,'-.','color','b','linewidth',2)
ylim([90 450])
ylabel('oxygen')
 
 
% new fronds
yyaxis right
hold on
plot(date_nf_off,newfrond,'.','markersize',37,'Color','r')  
ylabel('New Fronds')
ylim([-1.5 7])
ax=gca;     % make y axes black
ax.YAxis(1).Color='k'
ax.YAxis(2).Color='k'
set(gca,'fontsize',16)
x = datenum('June-27-2018'):7:datenum('Oct-3-2018');
 
set(gca, 'XTick', x);
datetick('x','mm/dd','keepticks');  
% set(gca,'XTickLabel','');

[Adam Danz]

You can scale the y-data to one of the y-axis ranges after setting ylim and then modify the y-tick-labels to show both scales.

An alternative is to create a second, transparent axes on top of the existing axes, use linkaxes(h,'x') and offset the y tick labels. I'd provide a demo but no access to Matlab at the moment.

[Heidi Hirsh]

Hey Adam,

By scaling the data do you mean replacing my current y values with values that fit one of my current axes at equal intervals. The axis I want to add has values from 0 to 5 (much smaller than the other two). See powerpoint mock up I attached.

I'm not sure how to set up transparent axes on top. Sorry!

[Adam Danz]

After plotting all of the data on the yyaxis, set the xlim and ylim so it doesn't change. That's important.

Let's say the new data you want to add on an independent y axis is called data and you want to scale it to the left yyaxis. Let's say that the values in data range from 0 to 5 but you want it in the middle of the y axis range as shown in the picture you shared.

The following are the basic steps you'll need to take. This is untested (again, I don't have access to Matlab right now).

1) Get the y-axis range for the left yyaxis

yyaxis left
leftAxisRange = ylim(); 

2) set the desired axis limits for the new data axis

data = 1:5;              % Your data values (I'm making these up)
dataAxisRange = [-3 7];  % these are the limits you'd like for the new axes

4) Now you have to scale data to the left yaxis range while factoring in the data axis range.

dataScaled = ((data - dataAxisRange(1)) / range(dataAxisRange)) * range(leftAxisRange) + leftAxisRange(1); 

5) plot the data using the left axis

yyaxis left
plot(x, dataScaled)

6) You'll have to add pseudo axis ticks that are really just text objects next to the axes.

xl = xlim(); 
yTicks = -1:6; 
% This next line is the same exact scaling we did above.
yTicksScaled = ((yTicks - dataAxisRange(1)) / range(dataAxisRange)) * range(leftAxisRange) + leftAxisRange(1); 
yTickXvals = repmat(xl(1), size(yTicksScaled)); 
yTickLabels = strsplit(num2str(yTicks)); 
text(yTickXvals, yTicksScaled, yTickLabels, 'HorizontalAlignment', 'Left')