[R] Signif. codes

My question is about the "Signif. codes" and the p-value, specifically, the output when I run summary(nameofregression.lm) So you get this little key: Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 And on a regression I ran, next to the intercept data, I get '***' Coefficients

[R] "Object is not a matrix" Error

I'm trying to follow this guide here: http://www.ats.ucla.edu/stat/r/modules/dummy_vars.htm In which I'm creating categorical variables using the factor function. I am able to go through the example listed above and have everything work, however, when I try to input my own numbers, I get an error