为什么group_by不能正确计算平均值？

Question

我有一个data.frame c，它有两个列a和b。我想将列 a 和平均列 b 分组。 但效果不太好

这是我的数据框和代码

> c
      a      b
1   Red  60822
2   Red 343855
3  Blue   5510
4  Blue   5633
5   Red    299
6  Blue     42
7  Blue    140
8   Red     29
9  Blue   3935
10  Red   6546
11 Blue     17
12 Blue  26400

> c %>% as_tibble() %>% group_by(a) %>% summarise(dd = mean(b))
     dd
1 37769

> class(c)
[1] "data.frame"

> str(c)
'data.frame':   12 obs. of  2 variables:
 $ a: chr  "Red" "Red" "Blue" "Blue" ...
 $ b: num  60822 343855 5510 5633 299 ...

还有Rversion、Dplyr包版本：

> R.version
               _                                
platform       x86_64-w64-mingw32               
arch           x86_64                           
os             mingw32                          
crt            ucrt                             
system         x86_64, mingw32                  
status                                          
major          4                                
minor          2.1                              
year           2022                             
month          06                               
day            23                               
svn rev        82513                            
language       R                                
version.string R version 4.2.1 (2022-06-23 ucrt)
nickname       Funny-Looking Kid  
> packageVersion("dplyr")
[1] ‘1.1.3’

Answer 1

更改为

cc = read.table(text = "      a      b
1   Red  60822
2   Red 343855
3  Blue   5510
4  Blue   5633
5   Red    299
6  Blue     42
7  Blue    140
8   Red     29
9  Blue   3935
10  Red   6546
11 Blue     17
12 Blue  26400", header = TRUE)

library(dplyr)
cc |>
  summarise(dd = mean(b), .by = a)

给予

     a        dd
1  Red 82310.200
2 Blue  5953.857