r - dplyr 自连接与过滤器

Question

我想从长格式数据框中所有其他标记的项目中减去带有标签“基线”的行中的值。使用带有“基线”子集的 left_join 可以很容易地通过两个步骤来完成此操作。但是，我不知道如何将 vas_1 和 vas_diff 组合成一个链。

library(dplyr)
# Create test data
n_users = 5
vas = data_frame(
  user = rep(letters[1:n_users], each = 3),
  group = rep(c("baseline", "early", "late" ),n_users),
  vas = round(rgamma(n_users*3, 10,1.4 ))
)
# The above data are given


# Assume some other operations are required
vas_1 = vas %>%
  mutate(
    vas = vas * 2
  )
# I want to put the following into one
# chain with the above
# Use self-join to subtract baseline
vas_diff = vas_1 %>%
  filter(group != "baseline") %>%
  # Problem is vas_1 here. Using . gives error here
  # Adding copy = TRUE does not help
#  left_join(. %>% filter(group == "baseline") , by = c("user")) %>%
  left_join(vas_1 %>% filter(group == "baseline") , by = c("user")) %>%
  mutate(vas = vas.x - vas.y) %>% # compute offset
  select(user, group.x, vas) # remove temporary variables

vas_diff

Answer 1

当 . 应该多次使用时，我使用匿名函数:

... %>% (function(df) { ... }) %>% ...

因此，就您而言:

vas_diff = vas_1 %>%
  filter(group != "baseline") %>%
  (function(df) left_join(df, df %>% filter(group == "baseline") , by = c("user"))) %>%
  mutate(vas = vas.x - vas.y) %>% # compute offset
  select(user, group.x, vas)

(这不会产生上面评论中描述的理想结果，但它展示了如何使用匿名函数)

但你可能想要这个:

vas_diff = vas_1 %>%
  left_join(
    x = filter(., group != "baseline")
    , y = filter(., group == "baseline")
    , by = c("user")
  ) %>%
  mutate(vas = vas.x - vas.y) %>% # compute offset
  select(user, group.x, vas) # remove temporary variables