R 文本连接 : "argument ' object' must deparse to a single character string"

Question

我想将字符串列表转换为数据框。 但是，我收到此错误:

> read.csv(textConnection(c("id,name,count",
                          '6289,aa,16',
                          '6269,bb,8',
                          '6269,cc,8',
                          '6269,dd,8',
                          '6610,ee,4')))
 Error in textConnection(c("id,name,count", "6289,aa,16", "6269,bb,8",  : 
  argument 'object' must deparse to a single character string
Calls: read.csv -> read.table -> textConnection

当我只删除一行时，它会起作用:

> read.csv(textConnection(c("id,name,count",
                          '6289,aa,16',
                          '6269,bb,8',
                          '6269,cc,8',
                          '6610,ee,4')))
   id name count
1 6289   aa    16
2 6269   bb     8
3 6269   cc     8
4 6610   ee     4

这是怎么回事？!

Answer 1

阿南达说得对，这种行为源于deparse。在 textConnection() 文档的“详细信息”部分下，显示:

object should be the name of a character vector: however, short expressions will be accepted provided they deparse to less than 60 bytes.

deparse() 将表达式转换为字符串。当表达式 deparse 超过 60 个字节时，deparse 会尝试将字符串拆分为较短的文本 block ；即字符串向量。尝试一下:

deparsed <- deparse(c("this expr","deparses to length=1,","nchar=57 bytes"))
deparsed
[1] "c(\"this expr\", \"deparses to length=1,\", \"nchar=57 bytes\")"
nchar(deparsed)
[1] 57

deparsed <- deparse(c("whereas this longer expression","deparses to length=2,","nchar=c(61,23) bytes"))
deparsed
[1] "c(\"whereas this longer expression\", \"deparses to length=2,\", "
[2] "\"nchar=c(61,23) bytes\")"
nchar(deparsed)
[1] 61 23

这就是您收到错误的原因

argument 'object' must deparse to a single character string

适合较长的表达，但不适合较短的表达。

正如 sds 和 Simon 所示，解决方案是将表达式分配给一个对象，然后对对象名称而不是原始表达式调用 textConnection。

txt <- c("id,name,count", '6289,aa,16', '6269,bb,8',
         '6269,cc,8', '6269,dd,8', '6610,ee,4')
read.csv(textConnection(txt))
    id name count
1 6289   aa    16
2 6269   bb     8
3 6269   cc     8
4 6269   dd     8
5 6610   ee     4

在后台，textConnection 现在调用 deparse(substitute(txt)) 而不是 deparse(substitute(c("id,name,count", ...))) 。只有较短的表达式才会分解为单个字符串。这就是 textConnection 所需要的。