Group_by（dplyr），其中一个因素作为列

Question

In the following dummy data set, I would like to create a summary table grouping over three variables. So far, I used dplyr . However, I would like to have the values of r as the column names, and the x1 and x2 valuesas the row names, with the respective cells filled by values from m. What could be a solution?

r <- rep(seq(1,10,1),10)
x1 <- rbinom(100, 1, 0.5)
x2 <- rbinom(100, 2, 0.5)
y <- rnorm(100, 10, 5)

df <- data.frame(r,x1,x2,y)

library(dplyr)

View(df %>% 
  group_by(x1,x2,r) %>% 
  summarise(m = mean(y))
)

Answer 1

In order to achieve your desired output you basically have to transform from long to wide fromat, using x1 and x2 as grouping variables. Function spread() will do the job:

library(dplyr)
library(tidyr)

df %>% 
  group_by(x1,x2,r) %>% 
  summarise(m = mean(y)) %>% 
  ungroup %>% 
  spread(key = r, value = m,-x1, -x2)