R sqldf将数字列按顺序更改为字符列

今天我发现了一个无法解释的问题。这是众所周知的行为吗

数据集：

structure(list(Original.Unit = c("some unit", "some unit", "some unit", 
"some unit", "some unit", "some unit"), Result = c(24, 28, NA, 
4.1, 4.5, 2.6), Conversion.Factor = c(1, 1.54, 1, 2.2, 1, 1)), .Names = c("Original.Unit", 
"Result", "Conversion.Factor"), row.names = c(NA, 6L), class = "data.frame")

代码：

为什么ConvResult列现在是character类型？这是因为NA吗

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看来这就是重点。当我将NA替换为1000时，结果变成了数字。但是为什么会这样呢？

是的，看来你是对的。使用orderby时，sqldf倾向于猜测输出列的类，在这种情况下会出错。因此，我想您可以自己设置列类型，以确保：

  result <- sqldf("SELECT `Original.Unit`, Result, `Conversion.Factor`, Result * `Conversion.Factor` AS ConvResult FROM data ORDER BY ConvResult",method = c("character", "numeric", "numeric", "numeric"))

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result变通方法，将结果排序到sqldf之外
result SQLite使用第一行来获取类型信息，在本例中，
ConvResult
的第一行是NA，因此无法识别。您可以使用H2后端尝试查询：
库（RH2）；sqldf（“…”）
感谢您的解释！sqldf暴露了更多的问题。它会丢失编码（或者更确切地说是将文本从UTF8编码为本地编码），有时会丢失POSIXct类等等。但我还是喜欢它：）因为我创建了“包装”sqldf并立即修复许多“问题”的函数sqldfEx，所以我将用这个函数更新它。谢谢
> (result <- sqldf("SELECT `Original.Unit`, Result, `Conversion.Factor`, Result * `Conversion.Factor` AS ConvResult FROM data"))
  Original.Unit Result Conversion.Factor ConvResult
1     some unit   24.0              1.00      24.00
2     some unit   28.0              1.54      43.12
3     some unit     NA              1.00         NA
4     some unit    4.1              2.20       9.02
5     some unit    4.5              1.00       4.50
6     some unit    2.6              1.00       2.60

> sapply(result, function(r) { class(r)})
    Original.Unit            Result Conversion.Factor        ConvResult 
      "character"         "numeric"         "numeric"         "numeric" 

> (result <- sqldf("SELECT `Original.Unit`, Result, `Conversion.Factor`, Result * `Conversion.Factor` AS ConvResult FROM data ORDER BY ConvResult"))
  Original.Unit Result Conversion.Factor ConvResult
1     some unit     NA              1.00       <NA>
2     some unit    2.6              1.00        2.6
3     some unit    4.5              1.00        4.5
4     some unit    4.1              2.20       9.02
5     some unit   24.0              1.00       24.0
6     some unit   28.0              1.54      43.12

> sapply(result, function(r) { class(r)})
    Original.Unit            Result Conversion.Factor        ConvResult 
      "character"         "numeric"         "numeric"       "character" 

  result <- sqldf("SELECT `Original.Unit`, Result, `Conversion.Factor`, Result * `Conversion.Factor` AS ConvResult FROM data ORDER BY ConvResult",method = c("character", "numeric", "numeric", "numeric"))