Many ways to do the same thing: linear regression

One feature of R (could be positive, could be negative) is that there are many ways to do the same thing. In this post, I list out the different ways we can get certain results from a linear regression model. Feel free to comment if you know more ways other than those listed!

In what follows, we will use the linear regression object lmfit:

data(mtcars)
lmfit <- lm(mpg ~ hp + cyl, data = mtcars)

Extracting coefficients of the linear model

# print the lm object to screen
lmfit

# part of the summary output
summary(lmfit)

# extract from summary output
summary(lmfit)$coefficients[, 1]

# use the coef function
coef(lmfit)

# extract using list syntax
lmfit$coefficients

Getting fitted values for the training data set

# use the predict function
predict(lmfit)

# extract from lm object
lmfit$fitted.values

Getting residuals for the training data set

# use the predict function
resid(lmfit)

# extract from lm object
lmfit$residuals

# extract from lm summary
summary(lmfit)$residuals