变异根据不同列的标准进行差异

Question

| weight    | Time     | Chick   | Diet    |
|-----------|----------|---------|---------|
|    42     |    0     |    1    |    1    |
|    51     |    2     |    1    |    1    |
|    59     |    4     |    1    |    1    |
|    64     |    6     |    1    |    1    |
|    76     |    8     |    1    |    1    |
|    93     |    10    |    1    |    1    |
|    106    |    12    |    1    |    1    |
|    125    |    14    |    1    |    1    |
|    149    |    16    |    1    |    1    |
|    171    |    18    |    1    |    1    |
|    199    |    20    |    1    |    1    |
|    205    |    21    |    1    |    1    |
|    40     |    0     |    2    |    1    |
|    49     |    2     |    2    |    1    |

我需要取当前的重量并在时间0减去重量。时间间隔每12行重置一次。将其变为WeightGain列。请帮我在r。

中这样做

Answer 1

我们根据时间0的出现创建一个分组变量，然后从第一个'权重'中减去'权重'

library(dplyr)
df1 %>% 
   group_by(grp = cumsum(Time==0)) %>%
   mutate(WeightGain = weight - first(weight))
# A tibble: 24 x 6
# Groups:   grp [2]
#   weight  Time Chick  Diet   grp newweight
#    <int> <int> <int> <int> <int>     <int>
# 1     42     0     1     1     1         0
# 2     51     2     1     1     1         9
# 3     59     4     1     1     1        17
# 4     64     6     1     1     1        22
# 5     76     8     1     1     1        34
# 6     93    10     1     1     1        51
# 7    106    12     1     1     1        64
# 8    125    14     1     1     1        83
# 9    149    16     1     1     1       107
#10    171    18     1     1     1       129
# ... with 14 more rows