dplyr与子组连接

Question

下面的问题可以看作是"两列重塑到宽",并且有几种方法可以解决它的经典方式,从base::reshape(恐怖)到reshape2.对于两组情况,一个简单的子组连接效果最好.

我可以在管道框架内重新构建连接dplyr吗？下面的例子有点傻,但我需要加入更长的管道链,我不想打破它.

library(dplyr)
d = data.frame(subject= rep(1:5,each=2),treatment=letters[1:2],bp = rnorm(10))

d %>%
  # Assume piped manipulations here
  # Make wide
  # Assume additional piped manipulations here

# Make wide (old style)
with(d,left_join(d[treatment=="a",],
          d[treatment=="b",],by="subject" ))

Answer 1

怎么样

d %>% 
  filter(treatment == "a") %>%
  left_join(., filter(d, treatment == "b"), by = "subject")

#  subject treatment.x       bp.x treatment.y      bp.y
#1       1           a  0.4392647           b 0.6741559
#2       2           a -0.6010311           b 1.9845774
#3       3           a  0.1749082           b 1.7678771
#4       4           a -0.3089731           b 0.4427471
#5       5           a -0.8346091           b 1.7156319

您可以在左连接后立即继续管道.

或者,如果您不需要单独的处理列,您可以使用tidyr来执行:

library(tidyr)
d %>% spread(treatment, bp)
#  subject          a         b
#1       1  0.4392647 0.6741559
#2       2 -0.6010311 1.9845774
#3       3  0.1749082 1.7678771
#4       4 -0.3089731 0.4427471
#5       5 -0.8346091 1.7156319

(这是与使用d %>% dcast(subject ~ treatment, value.var = "bp")从reshape2包通过的Henrik在评论中所指出)