# load the mtcars data
data(mtcars)

head(mtcars) # Look at the first 6 rows of your data 

##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

Create a constant

# we can create a constant that is always '1' 
mtcars$constant <- 1 
head(mtcars)

##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1
##                   constant
## Mazda RX4                1
## Mazda RX4 Wag            1
## Datsun 710               1
## Hornet 4 Drive           1
## Hornet Sportabout        1
## Valiant                  1

Create a variable from existing variables

# Ratio of horse power to cylinders
mtcars$hp_c <- mtcars$hp/mtcars$cyl
head(mtcars)

##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1
##                   constant  hp_c
## Mazda RX4                1 18.33
## Mazda RX4 Wag            1 18.33
## Datsun 710               1 23.25
## Hornet 4 Drive           1 18.33
## Hornet Sportabout        1 21.88
## Valiant                  1 17.50

Create a variable based on the values of existing variables

# dummy variable to indicate if a car gets more than 20 mpg
# use the "ifelse" command
# ifelse(condition, if meets condition give variable this value, otherwise give variable this value)
mtcars$mpg20 <- ifelse(mtcars$mpg > 20, 1, 0)
head(mtcars)

##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1
##                   constant  hp_c mpg20
## Mazda RX4                1 18.33     1
## Mazda RX4 Wag            1 18.33     1
## Datsun 710               1 23.25     1
## Hornet 4 Drive           1 18.33     1
## Hornet Sportabout        1 21.88     0
## Valiant                  1 17.50     0