R 随机 Select 的非NA列的行均数

我有一个数据框，其中对于每一行，我想随机抽样三列(其中三列可以因行而异)，并取这三个采样值的平均值.作为一个额外的问题，我有许多行完全是NA的(由于其他原因，我不能删除它们)，或者只包含1到2个非NA值.基于this question and answer分，我try 了以下几种方法:

df_new <- df %>%
  rowwise %>%
  mutate(inflo_mean = mean(sample(na.omit(c_across(everything())), 3)))

这不起作用，我得到一个关于使用sample()的错误:

Error in `mutate()`:
ℹ In argument: `inflo_mean = mean(sample(na.omit(c_across(everything())), 3))`.
ℹ In row 1.
Caused by error in `sample.int()`:
! invalid first argument

然后我试着把它分解成更小的步骤，分别处理不同的NA病例，并得出以下结论:

df_new2 <- df %>%
  rowwise() %>%
  mutate(num_NAs = sum(!is.na(across(starts_with("Col_")))),
         v_inflo = list(na.omit(c_across((starts_with("Col_"))))),
         inflo_mean = case_when(num_NAs > 2 ~ mean(sample(v_inflo, 3)),
                                  num_NAs == 2 ~ mean(v_inflo),
                                  num_NAs == 1 ~ as.numeric(v_inflo),
                                  num_NAs == 0 ~ NA_real_,
                                  TRUE ~ NA_real_))

同样，这也不起作用，我得到了相同的错误.我判断了列的数据类型，它们都是整数.这可能是什么问题呢？或者还有其他解决方案吗？

示例数据:

> dput(df)
structure(list(Col_1 = c(NA, 77L, 82L, 172L), Col_2 = c(NA, 79L, 
NA, 135L), Col_3 = c(NA, 81L, NA, 131L), Col_4 = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), Col_5 = c(NA, NA, NA, 
33L), Col_6 = c(NA, NA, NA, 104L), Col_7 = c(NA, NA, NA, 106L
), Col_8 = c(NA, NA, NA, 93L), Col_9 = c(NA, NA, NA, 50L), Col_10 = c(NA, 
NA, NA, 48L), Col_11 = c(NA, NA, NA, 96L), Col_12 = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), Col_13 = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), Col_14 = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), Col_15 = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_)), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -4L))