如何添加行以使每个组具有相等的行数？答案

【问题标题】：How to add rows so that each group has equal number of rows?如何添加行以使每个组具有相等的行数？
【发布时间】：2023-02-01 21:34:08
【问题描述】：

我有一个数据框，每组的行数不相等，请参见下面示例中的df。我想在所有其他列中添加包含组名和 NA 的行，以便每个组的行数与 df.desired 中的相同。这些行应添加到相应组的最后一行之后。

例子：

df = data.frame(group = c("A","A","A","A","B","B","B","C","C"),  
                         col1 = c(1, 1, 1, 1, 2, 2, 2, 3, 3),
                         col2 = c(12, 13, 14, 15, 21, 22, 23, 31, 32))
> df
  group col1 col2
1     A    1   12
2     A    1   13
3     A    1   14
4     A    1   15
5     B    2   21
6     B    2   22
7     B    2   23
8     C    3   31
9     C    3   32
df.desired = data.frame(group = c("A","A","A","A","B","B","B","B","C","C","C","C"),  
                         col1 = c(1, 1, 1, 1, 2, 2, 2, NA, 3, 3, NA, NA),
                         col2 = c(12, 13, 14, 15, 21, 22, 23, NA, 31, 32, NA, NA))
> df.desired
   group col1 col2
1      A    1   12
2      A    1   13
3      A    1   14
4      A    1   15
5      B    2   21
6      B    2   22
7      B    2   23
8      B   NA   NA
9      C    3   31
10     C    3   32
11     C   NA   NA
12     C   NA   NA

我知道如何使用循环来执行此操作，但这会非常慢，如果可能的话，我更愿意使用dplyr。有人有什么想法吗？

【问题讨论】：

标签： r dplyr

【解决方案1】：

这个怎么样：

library(dplyr)
df = data.frame(group = c("A","A","A","A","B","B","B","C","C"),  
               col1 = c(1, 1, 1, 1, 2, 2, 2, 3, 3),
               col2 = c(12, 13, 14, 15, 21, 22, 23, 31, 32))
maxgp <- max(table(df$group))

df %>% 
  group_by(group) %>% 
  summarise(across(everything(), ~c(.x, rep(NA, maxgp-n()))))
#> `summarise()` has grouped output by 'group'. You can override using the
#> `.groups` argument.
#> # A tibble: 12 × 3
#> # Groups:   group [3]
#>    group  col1  col2
#>    <chr> <dbl> <dbl>
#>  1 A         1    12
#>  2 A         1    13
#>  3 A         1    14
#>  4 A         1    15
#>  5 B         2    21
#>  6 B         2    22
#>  7 B         2    23
#>  8 B        NA    NA
#>  9 C         3    31
#> 10 C         3    32
#> 11 C        NA    NA
#> 12 C        NA    NA

^{由 reprex package (v2.0.1) 创建于 2023-02-01}

【讨论】：