I wonder what I am doing wrong here.

我想知道我在这里做错了什么。

I am trying to use case_when() with summarise() to get a summary for each, depending on the number of rows for each id.

我尝试结合使用case_When()和SUMMISE()来获取每个id的摘要，具体取决于每个id的行数。

library(dplyr, warn.conflicts = F)
mock <- tibble::tribble(~id, ~name, ~year,
                1, "xy", 2022,
                1, "xyz", 2021,
                2, "aaa", NA,
                3, "xaa", 2021)

mock %>% 
  group_by(id) %>% 
  summarise(
    condition = case_when(
      n() > 1 ~ "problem",
      .default = NA_character_
    ),
    name2 = case_when(
      n() == 1 ~ name,
      .default = NA_character_
    )
  )
#> Warning: Returning more (or less) than 1 row per `summarise()` group was deprecated in
#> dplyr 1.1.0.
#> ℹ Please use `reframe()` instead.
#> ℹ When switching from `summarise()` to `reframe()`, remember that `reframe()`
#>   always returns an ungrouped data frame and adjust accordingly.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
#> `summarise()` has grouped output by 'id'. You can override using the `.groups`
#> argument.
#> # A tibble: 4 × 3
#> # Groups:   id [3]
#>      id condition name2
#>   <dbl> <chr>     <chr>
#> 1     1 problem   <NA> 
#> 2     1 problem   <NA> 
#> 3     2 <NA>      aaa  
#> 4     3 <NA>      xaa

^{Created on 2023-09-09 with reprex v2.0.2}

创建于2023-09-09，Reprex v2.0.2

But I would just like to have :

但我只想要：

#> # A tibble: 3 × 3
#>      id condition name2
#>   <dbl> <chr>     <chr>
#> 2     1 problem   <NA> 
#> 3     2 <NA>      aaa  
#> 4     3 <NA>      xaa

case_when is used to iterate down a column and create a new vector based on the existing values in other columns. That's not what you are trying to do here. You are trying to conditionally choose a single output based on the group size, which is always a length-1 integer. Effectively, the value of n() gets recycled into a vector of the same length as the group size. If you want the output of summarize to be length one, you should use if and else, not case_when or if_else.

CASE_WHEN用于向下迭代一列，并基于其他列中的现有值创建新的向量。这不是你在这里试图做的事情。您正在尝试根据组大小有条件地选择单个输出，组大小始终是长度为-1的整数。实际上，n()的值被循环到一个与组大小相同长度的向量中。如果希望汇总的输出长度为1，则应该使用IF和ELSE，而不是CASE_WHEN或IF_ELSE。

mock %>% 
  group_by(id) %>% 
  summarize(
    condition = if(n() > 1) 'problem' else NA_character_, 
    name2     = if(n() == 1) name else NA_character_
  )
#> # A tibble: 3 x 3
#>      id condition name2
#>   <dbl> <chr>     <chr>
#> 1     1 problem   <NA> 
#> 2     2 <NA>      aaa  
#> 3     3 <NA>      xaa

^{Created on 2023-09-09 with reprex v2.0.2}

创建于2023-09-09，Reprex v2.0.2

You can use case_when like this:

您可以在如下所示的情况下使用Case_When：

using first() or [1] will overcome the issue explained by @Allan Cameron

使用first()或[1]可以解决@Allan Cameron解释的问题

library(dplyr)

mock %>% 
  group_by(id) %>% 
  summarise(
    condition = case_when(
      n() > 1 ~ "problem",
      TRUE ~ NA_character_
    ),
    name2 = case_when(
      # n() == 1 ~ name[1],
      n() == 1 ~ first(name),
      TRUE ~ NA_character_
    ),
    .groups = 'drop'
  )


   id condition name2
  <dbl> <chr>     <chr>
1     1 problem   NA   
2     2 NA        aaa  
3     3 NA        xaa  

Try this

尝尝这个

within(mock, {
  condition <- ave(name, id, FUN=\(x) switch(length(unique(x)), NA, 'problem'))
  name1 <- replace(name, !is.na(condition), NA)
  rm(name, year)
  }) |> unique()
#   id name1 condition
# 1  1  <NA>   problem
# 3  2   aaa      <NA>
# 4  3   xaa      <NA>

Data:

数据：

mock <- structure(list(id = c(1, 1, 2, 3), name = c("xy", "xyz", "aaa", 
"xaa"), year = c(2022, 2021, NA, 2021)), row.names = c(NA, -4L
), class = "data.frame")