CODEWITHSUNDEEP
rdplyr
BrooklynSon
BrooklynSon

Reputation: 2103

R how to use group_by to get averages per group

Using the mpg data set, I want to group by displacement (2.0 and 3.1).

So far I've only been able do the grouping without error:

data(mpg)

mpg2 <- filter(mpg, manufacturer == "audi" & year == 2008 & cyl < 8)

x <- group_by(mpg2, displ) 
    # %>% mutate(total_cty = {sum(.$cty)}) #new column getting the total of cty for each group (2.0, 3.1)
    # proportion = total_cty/total_cty_of.2.0 + total_cty_of.3.1

I know group_by alone doesn't change the appearance, except when you use aggregates on it like summarise. I would like to be able to see the new result though if possible.

Upvotes: 0

Views: 193

Answers (1)

Ronak Shah
Ronak Shah

Reputation: 389265

Don't use $ in dplyr pipes, very rarely they are useful. When you use that the groupings are lost.

We can calculate sum cty for each displ value and then calculate their proportion. 

library(dplyr)

mpg2 %>%
  group_by(displ) %>%
  summarise(cty = sum(cty)) %>%
  mutate(cty_prop = cty/sum(cty))

# displ   cty cty_prop
#  <dbl> <int>    <dbl>
#1   2      80    0.544
#2   3.1    67    0.456

Upvotes: 1

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