regex - 导入包含逗号、千位分隔符和尾随减号的 CSV 数据

Question

Mac OS X 上的 R 2.13.1。我正在尝试导入一个数据文件，其中包含千位分隔符和逗号作为小数点，以及负值的尾随减号。

基本上，我正在尝试转换:

"A|324,80|1.324,80|35,80-"

至

  V1    V2     V3    V4
1  A 324.80 1324.8 -35.80

现在，以交互方式执行以下两项操作:

gsub("\\.","","1.324,80")
[1] "1324,80"

gsub("(.+)-$","-\\1", "35,80-")
[1] "-35,80"

并将它们组合起来:

gsub("\\.", "", gsub("(.+)-$","-\\1","1.324,80-"))
[1] "-1324,80"

但是，我无法从 read.data 中删除千位分隔符:

setClass("num.with.commas")

setAs("character", "num.with.commas", function(from) as.numeric(gsub("\\.", "", sub("(.+)-$","-\\1",from))) )
mydata <- "A|324,80|1.324,80|35,80-"

mytable <- read.table(textConnection(mydata), header=FALSE, quote="", comment.char="", sep="|", dec=",", skip=0, fill=FALSE,strip.white=TRUE, colClasses=c("character","num.with.commas", "num.with.commas", "num.with.commas"))

Warning messages:
1: In asMethod(object) : NAs introduced by coercion
2: In asMethod(object) : NAs introduced by coercion
3: In asMethod(object) : NAs introduced by coercion

mytable
  V1 V2 V3 V4
1  A NA NA NA

请注意，如果我从“\\.”更改为“\\.”到函数中的“，”，事情看起来有点不同:

setAs("character", "num.with.commas", function(from) as.numeric(gsub(",", "", sub("(.+)-$","-\\1",from))) )

mytable <- read.table(textConnection(mydata), header=FALSE, quote="", comment.char="", sep="|", dec=",", skip=0, fill=FALSE,strip.white=TRUE, colClasses=c("character","num.with.commas", "num.with.commas", "num.with.commas"))

mytable
  V1    V2     V3    V4
1  A 32480 1.3248 -3580

我认为问题在于 read.data with dec=","将传入的“,”转换为“.”在调用 as(from, "num.with.commas") 之前，以便输入字符串可以是例如“1.324.80”。

我希望 as("1.123,80-","num.with.commas") 返回 -1123.80 和 as("1.100.123,80", "num.with.commas") 返回 1100123.80。

如何让我的 num.with.commas 替换输入字符串中除最后一个小数点之外的所有小数点？

更新:首先，我添加了否定前瞻并让 as() 在控制台中工作:

setAs("character", "num.with.commas", function(from) as.numeric(gsub("(?!\\.\\d\\d$)\\.", "", gsub("(.+)-$","-\\1",from), perl=TRUE)) )
as("1.210.123.80-","num.with.commas")
[1] -1210124
as("10.123.80-","num.with.commas")
[1] -10123.8
as("10.123.80","num.with.commas")
[1] 10123.8

但是，read.table仍然存在同样的问题。在我的函数中添加一些 print() 表明 num.with.commas 实际上得到了逗号而不是要点。

所以我当前的解决方案是将“，”替换为“。”以 num.with.commas 表示。

setAs("character", "num.with.commas", function(from) as.numeric(gsub(",","\\.",gsub("(?!\\.\\d\\d$)\\.", "", gsub("(.+)-$","-\\1",from), perl=TRUE))) )
mytable <- read.table(textConnection(mydata), header=FALSE, quote="", comment.char="", sep="|", dec=",", skip=0, fill=FALSE,strip.white=TRUE, colClasses=c("character","num.with.commas", "num.with.commas", "num.with.commas"))
mytable
  V1    V2      V3    V4
1  A 324.8 1101325 -35.8

Answer 1

您应该先删除所有句点，然后将逗号更改为小数点，然后再使用 as.numeric() 进行强制转换。您稍后可以使用 options(OutDec=",") 控制小数点的打印方式。我不认为 R 在内部使用逗号作为小数分隔符，即使在传统的语言环境中也是如此。

> tst <- c("A","324,80","1.324,80","35,80-")
> 
> as.numeric( sub("\\,", ".", sub("(.+)-$","-\\1", gsub("\\.", "", tst)) ) )
[1]     NA  324.8 1324.8  -35.8
Warning message:
NAs introduced by coercion