How to use polyfit for a table of values

I am trying to fit a curve to data i read in from a excel file. This is the code i have so far. I've been trying to debug it for some time and the line that is giving me problems is when i use polyfit. The values that it gives for constants are NAN and NAN.

cardatatable = xlsread('carmpg.csv')
mpg = cardatatable(:,1);
horsepower = cardatatable(:,4);

figure(1)
plot(mpg,horsepower,'o')
xlabel('miles per gallon')
ylabel('horsepower')

p = polyfit(mpg,horsepower,1);
mpgfit = linspace(min(mpg),max(mpg),1000);
horsepowerfit = polyval(P,mpgfit);
hold on 
plot(mpgfit,horsepowerfit,1)

Answer 1

[Matt J]

That would occur if mpg or horsepower contain NaNs. You should remove them.

[Daniel Ibarra]

Thank you, this fixed the issue.

[Matt J]

You're welcome, but please Accept-click the answer if it resolved your question.