聚合列 - 如何处理不均匀的数据帧

我想聚合每个Chr每第三行（三行的总和）。然而，自从我的df不能被 3 整除，我不知道如何处理最后剩下的行，它可能只是 1 或 2 行。如果还剩下两行，我想将剩下的两行相加。

• Input

data.frame(Chr = c("chr1","chr1","chr1","chr1","chr1","chr2","chr2","chr2","chr2","chr2","chr3"),
           value = c(1,3,1,3,5,6,3,1,3,5,0),
           seq = c(1,2,3,4,5,1,2,3,4,5,6))

• 输出（使用dplyr mutate，保留所有列）

data.frame(Chr = c("chr1","chr1","chr1","chr1","chr1","chr2","chr2","chr2","chr2","chr2","chr3"),
           value = c(1,3,1,3,5,6,3,1,3,5,0),
           seq = c(1,2,3,4,5,1,2,3,4,5,6),
           agg = c(5,5,5,8,8,10,10,10,8,8,8))

您可以使用(row_number()-1) %/% 3每 3 个观察值进行分组。

library(dplyr)

df %>%
  mutate(Grp = (row_number()-1) %/% 3 + 1, .by = Chr) %>%
  mutate(agg = sum(value), .by = c(Chr, Grp))

#     Chr value seq Grp agg
# 1  chr1     1   1   1   5
# 2  chr1     3   2   1   5
# 3  chr1     1   3   1   5
# 4  chr1     3   4   2   8
# 5  chr1     5   5   2   8
# 6  chr2     6   1   1  10
# 7  chr2     3   2   1  10
# 8  chr2     1   3   1  10
# 9  chr2     3   4   2   8
# 10 chr2     5   5   2   8
# 11 chr3     0   6   1   0

If the Grp不需要列，您可以将其删除select(-Grp).