Including the dependent variable in your data to perform principal component analysis? Let's say you have a data set with GPA (dependent variable) and Amount of alcohol, Amount of study, IQ, and SAT score as the independent variables. And you want to perform the principal component analysis in R for dimension reduction.

In the csv file you read in R, do you have to have GPA or do you have to remove it?
You need to remove the dependent variable before performing PCA.
Otherwise you are essentially using the dependent variable to explain itself.

Also, think about prediction:
You might want to use your model to predict unknown GPA scores based on information about amount of alcohol, amount of study, IQ and SAT. In that case, it is impossible to include information on GPA scores.