r - 通过基于 R 中的键减去值来创建新列？

Question

我有一个这样的数据表

ID      DAYS    FREQUENCY
"ads"   20      3
"jwa"   45      2
"mno"   4       1
"ads"   13      3
"jwa"   60      2
"ads"   18      3

我想添加一个列，根据id减去最接近的天数。我的新表会像这样:

ID      DAYS    FREQUENCY    DAYS DIFF
"ads"   20      3            2 (because 20-18) 
"jwa"   45      2            NA (because no value greater than 45 for that id)
"mno"   4       1            NA
"ads"   13      3            NA
"jwa"   60      2            15
"ads"   18      3            5

奖励:有没有办法使用合并功能？

Answer 1

这是使用 dplyr 的答案:

require(dplyr)
mydata %>%
  mutate(row.order = row_number()) %>% # row numbers added to preserve original row order
  group_by(ID) %>%
  arrange(DAYS) %>%
  mutate(lag = lag(DAYS)) %>%
  mutate(days.diff = DAYS - lag) %>%
  ungroup() %>%
  arrange(row.order) %>%
  select(ID, DAYS, FREQUENCY, days.diff)

输出:

      ID  DAYS FREQUENCY days.diff
  <fctr> <int>     <int>     <int>
1    ads    20         3         2
2    jwa    45         2        NA
3    mno     4         1        NA
4    ads    13         3        NA
5    jwa    60         2        15
6    ads    18         3         5