Problem using polyfit with NaN data

Trying to find Young's Modulus in a specific range. I was to plot the the data for that range, but when I try to get the slope value, it gives me NaN. I worked on the code for days and tried various methods and loopholes, but I can't seem to get it.

data = readtable('TITLE.txt','ReadVariableNames',true);
Load = data.Load(1:end); 
Displacement = data.Displacement(1:end);
Strain = data.Strain(1:end);


Strain(Strain < 0.001) = NaN;
    plot(Strain)

Strain(Strain > 0.003) = NaN;
    plot(Strain)   

    
p = plot(Strain, Load, '.', 'color','r')
title('Youngs Modulus','FontSize', 20);
xlabel('Strain (in/in)', 'FontSize', 15);
ylabel('Load(lbf)', 'FontSize', 15);


polyfit(Strain, Load, 1)
polyval(Strain, Load)

Answer 1

[Jon]

To avoid having NaN in polyfit I would use

iFit = isfinite(Strain)
c = polyfit(Strain(iFit),Load(iFit))

% ok to have NaN when calculating fitted Load
yfit = polyval(c,Strain)

By the way shouldn't Young's Moduls use Tensile Stress (Load/Area) rather than just raw load?

[Jade Pearson]

I had to change it to

c = polyfit(Strain(iFit),Load(iFit),1)

but it worked! Thank you

[Jon]

Sorry, for the typo. If this solves your problem when you get a chance please accept the answer so others who might have a similar issue will know an answer is available

[Jon]

Thanks - One last style point for the future, the MATLAB answers site encourages brief titles for questions with just the essense of the problem, e.g. Problem using polyfit with NaN data, and then putting the details into the body of the question. Not a big thing but it makes it a little easier to look through the questions if they have brief titles.

[Jade Pearson]

Understandable. Thank you, I will remember that.

[Jon]

Very nice - I didn't realize you could edit the original question title. Looks very clean now!