读取数据框时，为什么列名中出现X.？ [英] Why am I getting X. in my column names when reading a data frame?

问题描述

我问了几个月前对此问题的疑问，我以为答案已经解决了我的问题，但是我又遇到了问题，解决方案对我不起作用。

I asked a question about this a few months back, and I thought the answer had solved my problem, but I ran into the problem again and the solution didn't work for me.

我正在导入CSV：

orders <- read.csv("<file_location>", sep=",", header=T, check.names = FALSE)

这是数据框的结构：

str(orders)

'data.frame':   3331575 obs. of  2 variables:
 $ OrderID  : num  -2034590217 -2034590216 -2031892773 -2031892767 -2021008573 ...
 $ OrderDate: Factor w/ 402 levels "2010-10-01","2010-10-04",..: 263 263 269 268 301 300 300 300 300 300 ...

如果我在第一列OrderID上运行 length 命令，我得到以下信息：

If I run the length command on the first column, OrderID, I get this:

length(orders$OrderID)
[1] 0

如果我运行 length 在OrderDate上，它会正确返回：

If I run the length on OrderDate, it returns correctly:

length(orders$OrderDate)
[1] 3331575

这是 CSV 的> head 。

This is a copy/paste of the head of the CSV.

OrderID,OrderDate
-2034590217,2011-10-14
-2034590216,2011-10-14
-2031892773,2011-10-24
-2031892767,2011-10-21
-2021008573,2011-12-08
-2021008572,2011-12-07
-2021008571,2011-12-07
-2021008570,2011-12-07
-2021008569,2011-12-07

现在，如果我重新运行 read.csv ，但是取出 .names 选项，数据框的第一列现在在名称的开头带有X。

Now, if I re-run the read.csv, but take out the check.names option, the first column of the dataframe now has an X. at the start of the name.

orders2 <- read.csv("<file_location>", sep=",", header=T)

str(orders2)

'data.frame':   3331575 obs. of  2 variables:
 $ X.OrderID: num  -2034590217 -2034590216 -2031892773 -2031892767 -2021008573 ...
 $ OrderDate: Factor w/ 402 levels "2010-10-01","2010-10-04",..: 263 263 269 268 301 300 300 300 300 300 ...

length(orders$X.OrderID)
[1] 3331575

此功能正常。

我的问题是为什么 R 在第一列名称的开头添加X。从CSV文件中可以看到，没有特殊字符。它应该是一个简单的负载。添加 check.names 会从CSV导入名称，但会导致数据无法正确加载，无法执行分析。

My question is why does R add an X. to beginning of the first column name? As you can see from the CSV file, there are no special characters. It should be a simple load. Adding check.names, while will import the name from the CSV, will cause the data to not load correctly for me to perform analysis on.

该如何解决？

侧面说明：我知道这是未成年人-我是我对我认为自己加载正确但没有得到预期的结果感到沮丧。我可以使用 colnames（orders）[1]<- OrderID 重命名该列，但仍然想知道为什么它不能正确加载。

Side note: I realize this is a minor - I'm just more frustrated by the fact that I think I am loading correctly, yet not getting the result I expected. I could rename the column using colnames(orders)[1] <- "OrderID", but still want to know why it doesn't load correctly.

推荐答案

read.csv（）是更一般的包装 read.table（）函数。后一个函数具有参数 check.names ，记录为：

read.csv() is a wrapper around the more general read.table() function. That latter function has argument check.names which is documented as:

check.names: logical.  If ‘TRUE’ then the names of the variables in the
         data frame are checked to ensure that they are syntactically
         valid variable names.  If necessary they are adjusted (by
         ‘make.names’) so that they are, and also to ensure that there
         are no duplicates.

如果标题包含语法上无效的标签，则 make.names（）将根据无效名称将其替换为有效名称，删除无效字符并可能在 X 之前：

If your header contains labels that are not syntactically valid then make.names() will replace them with a valid name, based upon the invalid name, removing invalid characters and possibly prepending X:

R> make.names("$Foo")
[1] "X.Foo"

这在？make.names 中记录：

Details:

    A syntactically valid name consists of letters, numbers and the
    dot or underline characters and starts with a letter or the dot
    not followed by a number.  Names such as ‘".2way"’ are not valid,
    and neither are the reserved words.

    The definition of a _letter_ depends on the current locale, but
    only ASCII digits are considered to be digits.

    The character ‘"X"’ is prepended if necessary.  All invalid
    characters are translated to ‘"."’.  A missing value is translated
    to ‘"NA"’.  Names which match R keywords have a dot appended to
    them.  Duplicated values are altered by ‘make.unique’.

您看到的行为与记录的方式完全一致 read.table（）会加载数据。这表明您在CSV文件的标题行中语法上无效的标签。注意上面？make.names 中的一点，什么是字母取决于系统的语言环境； CSV文件中可能包含您的文本编辑器将显示的有效字符，但是，如果R不是在相同的语言环境中运行，则该字符在那里可能无效，例如？

The behaviour you are seeing is entirely consistent with the documented way read.table() loads in your data. That would suggest that you have syntactically invalid labels in the header row of your CSV file. Note the point above from ?make.names that what is a letter depends on the locale of your system; The CSV file might include a valid character that your text editor will display but if R is not running in the same locale that character may not be valid there, for example?

我将查看CSV文件并在标题行中识别所有非ASCII字符；标头行中也可能有不可见的字符（或转义序列； \t ？）。在读取具有无效名称的文件与在控制台中显示文件之间可能发生了很多事情，这可能掩盖了无效字符，因此请不要误以为如果没有 check.names 表示文件正常。

I would look at the CSV file and identify any non-ASCII characters in the header line; there are possibly non-visible characters (or escape sequences; \t?) in the header row also. A lot may be going on between reading in the file with the non-valid names and displaying it in the console which might be masking the non-valid characters, so don't take the fact that it doesn't show anything wrong without check.names as indicating that the file is OK.

发布 sessionInfo（ ）也会有用。

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