R中如何結合tryCatch和If-Else語句？

Question

目的

我有數百本 Excel 練習冊。 其中大多數都有一張紙，比如“正確的紙”。 這些工作表都應該有 10 列。 我想將它們全部組合成一個統一的數據集（最終數據集）。

但是，某些工作簿沒有正確的工作表，加載它們時出現錯誤。 我確實有正確的工作表，其中一些沒有 10 列。 我想排除任何沒有正確工作表或正確工作表沒有 10 列的工作簿。

試圖

假設正確的工作表是一個數值變量。 因此，在下面的兩個變量中，只有“b”是正確的，因為它具有數值。 a = "你好" b = 8

代表

a <- "hello"
b <- 8


#A: Check that a + 2 does not produce an error
if(tryCatch({a + 2}, error = function(e) {"error"}) != "error") {
  
  #A1:If a+2 does not produce an error, then check that the sum is right
  if(a+2 == 10) {
    print("a No error and produced correct answer - Add 'a' to consolidated list")
  } else {
    
    #B: Check that b + 2 does not produce an error
    if(tryCatch({b+2}, error = function(e) {"error"}) != "error") {
      
      #B1:If b+2 does not produce an error, then check that the sum is right
      if(b+2 == 10) {
        print("a No error but produced wrong answer, 
              b No error and produced correct answer,
              Add 'b' to consolidated list")
      } else {
        print("a No error but produced wrong answer, b No error but produced wrong answer")
      }
      #B2: If b+2 produced an error
    } else {print("a No error but produced wrong answer, b Error")}
  }
  
  #A2:If a+2 produces an error, then go straight to b
} else {
    
    #B: Check that b + 2 does not produce an error
    if(tryCatch({b+2}, error = function(e) {"error"}) != "error") {
      
      #B1:If b+2 does not produce an error, then check that the sum is right
      if(b+2 == 10) {
        print("a Error, 
              b No error and produced correct answer, 
              Add 'b' to consolidated list")
      } else {
        print("a Error, b No error but produced wrong answer")
      }
      #B2: If b+2 produced an error
    } else {print("a Error, b Error")}
  }

問題

我實際上有三個變量（例如 a =“你好”，b = 8 和 c =“再見”，這增加了上述復雜性。

有更簡單的方法嗎？

Answer 1

您可以嘗試purrr::safely() 。 下面是一個使用“Excel 工作簿”嵌套列表的模擬示例：

library(purrr)

# example "workbooks"
wkbks <- list(
  w1 = list(
    sheet1 = 1:3,
    `Correct Sheet` = 1:10
  ),
  w2 = list(
    sheet1 = 1:3
  ),
  w3 = list(
    `Correct Sheet` = 1:8
  ),
  w4 = list(
    `Correct Sheet` = 1:10,
    sheet2 = 1:5
  )
)

# helper function to read wkbk and throw error conditions not met
read_correct <- function(x) {
  stopifnot(length(x[["Correct Sheet"]]) == 10)
  x[["Correct Sheet"]]
}

# iterate over wkbks, wrapping `read_correct` in `safely()`
correct_sheets <- wkbks |>
  map(safely(read_correct)) |>
  transpose()

結果：

# see all errors, removing NULLs
#> compact(correct_sheets$error)
$w2
<simpleError in .f(...): length(x[["Correct Sheet"]]) == 10 is not TRUE>

$w3
<simpleError in .f(...): length(x[["Correct Sheet"]]) == 10 is not TRUE>

# see all correct results, removing NULLs
#> compact(correct_sheets$result)
$w1
 [1]  1  2  3  4  5  6  7  8  9 10

$w4
 [1]  1  2  3  4  5  6  7  8  9 10