每个子组的交替行的差异相同

Question

我有一个数据框，我需要在其中找到差异，但是对于每个交替行，差异应该保持不变，因为要做的事情是一样的，就像这样：

但我用过这个：

things <- data.frame( category = c("A","B","A","B","A","B","A","B","A","B"),
                      things2do = c("ball","ball","bat","bat","hockey","hockey","volley ball","volley ball","foos ball","foos ball"),
                      number = c(12,5,4,1,0,2,2,0,0,2))


    things %>% 
      mutate(diff = number - lead(number,order_by=things2do))

但这没有帮助，因为我得到了这个：

我可以得到一些帮助吗？

Answer 1

library(tidyverse)

things2 <- things %>%
  spread(category, number) %>%
  mutate(diff = B - A) %>%
  gather(category, number, A:B) %>%
  select(category, things2do, number, diff) %>%
  arrange(things2do)

Answer 2

一种方法是按 things2do 对数据进行分组，然后进行迭代差分。

library(dplyr)
things %>% 
  group_by(things2do) %>%
  mutate(diff = diff(number))

每个子组的交替行的差异相同

Same difference in alternate rows per sub group

r

dplyr

row

difference

alternate