Calculate-the-Mean-by-Group-average.R

#Calculate the Mean by Group average
#create data frame
df <- data.frame(team=c('a', 'a', 'b', 'b', 'b', 'c', 'c'),
                 pts=c(5, 8, 14, 18, 5, 7, 7),
                 rebs=c(8, 8, 9, 3, 8, 7, 4))
df

##   team pts rebs
## 1    a   5    8
## 2    a   8    8
## 3    b  14    9
## 4    b  18    3
## 5    b   5    8
## 6    c   7    7
## 7    c   7    4

###method_1 aggregate
#find mean points scored by team
aggregate(df[,2:3], list(team = df$team), FUN=mean)

##   team      pts     rebs
## 1    a  6.50000 8.000000
## 2    b 12.33333 6.666667
## 3    c  7.00000 5.500000

###method_2 '
library(dplyr) 

## 
## 载入程辑包：'dplyr'

## The following objects are masked from 'package:stats':
## 
##     filter, lag

## The following objects are masked from 'package:base':
## 
##     intersect, setdiff, setequal, union

#find mean points scored by team 
df %>%
  group_by(team) %>%
  summarise_at(vars(pts), list(name = mean))

## # A tibble: 3 x 2
##   team   name
##   <chr> <dbl>
## 1 a       6.5
## 2 b      12.3
## 3 c       7

#ref  https://www.statology.org/r-mean-by-group/