如何在lm（）中删除R中的特定类别预测变量？

Question

I am just starting out on linear modelling . I have the below regressor

regressor=lm(Profit~R.D.Spend+Administration+Marketing.Spend+State,data=dataset)

Now three state levels.

> levels(dataset$State)
[1] "1" "2" "3"

Below is the output of my model , and i just need to remove state2 from it . How do i go about that ?

> summary(regressor)

Call:
lm(formula = Profit ~ R.D.Spend + Administration + Marketing.Spend + 
    State, data = dataset)

Residuals:
   Min     1Q Median     3Q    Max 
-33504  -4736     90   6672  17338 

Coefficients:
                  Estimate Std. Error t value Pr(>|t|)    
(Intercept)      5.013e+04  6.885e+03   7.281 4.44e-09 ***
R.D.Spend        8.060e-01  4.641e-02  17.369  < 2e-16 ***
Administration  -2.700e-02  5.223e-02  -0.517    0.608    
Marketing.Spend  2.698e-02  1.714e-02   1.574    0.123    
State2           1.988e+02  3.371e+03   0.059    0.953    
State3          -4.189e+01  3.256e+03  -0.013    0.990 

Answer 1

this should do it:

regressor<-update(regressor,~.-State2)
summary(regressor)