R 中的字符串操作:如何使用 cat(...,sep=" ") 打印但省略最后一个 space?

String manipulation in R: How to print with cat(...,sep=" ") but omit the last space?

我正在使用 R 打印 MPLUS 命令。我必须指定许多变量之间的协方差。因此,我必须创建一个集合的所有子集。在 MPLUS 中,它必须像这样指定(如果我们考虑 4 个变量 female、age、edu migrant 的列表):

female WITH age edu migrant;
age WITH edu migrant;
edu WITH migrant;

代表 4 个变量集的大小为 2 的所有子集(female WITH age;female WITH edu;female WITH migrant;age WITH edu;age WITH migrant;edu WITH migrant;)。

为了获得可以直接复制到 MPLUS 中的输出,我使用了命令 cat()。不幸的是,我无法得到上面显示的输出,只能得到这个输出(注意分号):

female WITH age edu migrant ;
age WITH edu migrant ;
edu WITH migrant ;

我经常使用 paste、cat 和 print。但是要么我在行尾的分号之前得到一个 space 的输出(就像上面直接的那样),要么我得到这个:

female WITH ageedumigrant;
age WITH edumigrant;
edu WITH migrant; 

所以我的问题基本上是:如何省略 cat(...,sep=" ") 命令中的最后一个 space?

我的小函数是这样的:

library(stringr)
vars_b <- "female age edu migrant"

covstructure <- function(x, cov = TRUE, var = TRUE, width = 80) {

  # decode variable list into a vector, e.g. x[1] = "female" #
  x <- gsub("(?<=[\s])\s*|^\s+|\s+$", "", x, perl=TRUE)
  x <- unlist(strsplit(x, " "))

  # covariance structure (the part of interest here) #
  if(cov==TRUE) {

    # all combinations #
    result <- combn(x,2)

    # get subsets into the MPLUS format: #
    # female WITH age edu migrant; #
    # age WITH edu migrant; #
    # edu WITH migrant; #

    for(i in 1:(length(x)-1)) {

      # indices of the combinations that include the i-th variable #
      ind <- which(result==x[i])

      # print variable WITH its combinations #
      # here is my problem: #
      cat(result[which.min(ind)], "WITH", result[ind+1], ";", fill=width)

      # create new combinations without the combinations of preceding variables, i.e. 1 to i #
      if(i < length(x)-1) { result <- combn(x[-c(1:i)],2) }
    }
  }

  # variance structure (not of interest) #
  if(var==TRUE) {
    cat(x, "", sep="; ", fill=width)
  }
}

covstructure(vars_b, cov=TRUE, var=FALSE)

我希望我能足够仔细地列出问题(这完全是关于 R 字符串操作)并提前非常感谢你。

以下代码对您有用吗?

x <- c("female", "WITH", "age", "edu", "migrant")
cat(cat(x), ";", sep="")

这可能是一个很好的方法 -

x <- c("female", "WITH", "age", "edu", "migrant")
y<-do.call(paste, c(as.list(x), sep=" "))
k<-paste(y,";",sep="")

现在字符串 k 将成为您想要的字符串 -

[1] "female WITH age edu migrant;"