r - Using mtcars data to make a summarised table of cylinders versus centered(mpg)

Question

Bare with me... I am using the R/RStudio with the data mtcars, dplyr , mutate and the summarise commands. Also tried group by.

I want to center the values mtcars$mpg then take that info and display the summary of the number of cylinders vs centered mtcars$mpg.

So far...

mtcars %>% mutate(centered_mpg = mpg - mean(mpg, na.rm = TRUE)) %>% summarise(centered_mpg, cyl)

The above produces:

centered_mpg	cyl
0.909375	6
0.909375	6
2.709375	4
1.309375	6
...	...

Answer 1

Are you looking for this?

with(mtcars, aggregate(list(centered_mpg=scale(mpg, scale=FALSE)), list(cyl=cyl), mean))
#   cyl centered_mpg
# 1   4    6.5730114
# 2   6   -0.3477679
# 3   8   -4.9906250