仅在“夹在中间"的情况下填写NA使用dplyr设置相同的值 [英] NA filling only if "sandwiched" by the same value using dplyr

问题描述

好，这是另一个缺少价值的问题.

Ok, here is yet another missing value filling question.

我正在寻找一种基于列中上一个和下一个存在的值来填充NA的方法.单一方向的标准填充不足以完成此任务.

I am looking for a way to fill NAs based on both the previous and next existent values in a column. Standard filling in a single direction is not sufficient for this task.

如果列中的上一个和下一个有效值不相同，则该块将保持为NA.

If the previous and next valid values in a column are not the same, then the chunk remains as NA.

示例数据框的代码为:

df_in <- tibble(id= 1:12,
        var1 = letters[1:12],
        var2 = c(NA,rep("A",2),rep(NA,2),rep("A",2),rep(NA,2),rep("B",2),NA))

谢谢

推荐答案

比较na.locf()(最后观察到的结转)和na.locf(fromLast = TRUE)(后退):

Comparing na.locf() (last observation carried forward) and na.locf(fromLast = TRUE) (backward):

mutate(df_in, 
       var_new = if_else(
         zoo::na.locf(var2, na.rm = FALSE) == 
           zoo::na.locf(var2, na.rm = FALSE, fromLast = TRUE),
         zoo::na.locf(var2, na.rm = FALSE),
         NA_character_
       ))

# # A tibble: 12 x 4
#       id var1  var2  var_new
#    <int> <chr> <chr> <chr>  
#  1     1 a     NA    NA     
#  2     2 b     A     A      
#  3     3 c     A     A      
#  4     4 d     NA    A      
#  5     5 e     NA    A      
#  6     6 f     A     A      
#  7     7 g     A     A      
#  8     8 h     NA    NA     
#  9     9 i     NA    NA     
# 10    10 j     B     B      
# 11    11 k     B     B      
# 12    12 l     NA    NA 

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