如何使用dplyr划分行组？

Question

我有这个数据帧:

x <- data.frame(
    name = rep(letters[1:4], each = 2),
    condition = rep(c("A", "B"), times = 4),
    value = c(2,10,4,20,8,40,20,100)
) 
#   name condition value
# 1    a         A     2
# 2    a         B    10
# 3    b         A     4
# 4    b         B    20
# 5    c         A     8
# 6    c         B    40
# 7    d         A    20
# 8    d         B   100

我想组名称和分列的值与condition == "B"那些用condition == "A",要得到这样的:

data.frame(
    name = letters[1:4],
    value = c(5,5,5,5)
)
#   name value
# 1    a     5
# 2    b     5
# 3    c     5
# 4    d     5

我知道这样的事情可以让我非常接近:

x$value[which(x$condition == "B")]/x$value[which(x$condition == "A")]

但我想知道是否有一个简单的方法来使用dplyr(我的数据框是一个玩具示例,我通过链接多个group_by和summarise调用来达到它).

Answer 1

尝试:

x %>% 
  group_by(name) %>%
  summarise(value = value[condition == "B"] / value[condition == "A"])

这使:

#Source: local data frame [4 x 2]
#
#    name value
#  (fctr) (dbl)
#1      a     5
#2      b     5
#3      c     5
#4      d     5

Answer 2

我用的spread是tidyr.

library(dplyr)
library(tidyr)

x %>%
  spread(condition, value) %>%
  mutate(value = B/A)

  name  A   B value
1    a  2  10     5
2    b  4  20     5
3    c  8  40     5
4    d 20 100     5

然后,您可以select(-A, -B)删除额外的列.