在R中正确使用gsub /正则表达式？

Question

我有很长的字符串列表,例如这个机器可读的例子:

A <- list(c("Biology","Cell Biology","Art","Humanities, Multidisciplinary; Psychology, Experimental","Astronomy & Astrophysics; Physics, Particles & Fields","Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods","Geriatrics & Gerontology","Gerontology","Management","Operations Research & Management Science","Computer Science, Artificial Intelligence; Computer Science, Information Systems; Engineering, Electrical & Electronic","Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods; Statistics & Probability"))  

所以它看起来像这样:

> A  
[[1]]  
 [1] "Biology"  
 [2] "Cell Biology"  
 [3] "Art"  
 [4] "Humanities, Multidisciplinary; Psychology, Experimental"  
 [5] "Astronomy & Astrophysics; Physics, Particles & Fields"  
 [6] "Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods"  
 [7] "Geriatrics & Gerontology"  
 [8] "Gerontology"  
 [9] "Management"  
[10] "Operations Research & Management Science"  
[11] "Computer Science, Artificial Intelligence; Computer Science, Information Systems; Engineering, Electrical & Electronic"  
[12] "Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods; Statistics & Probability"  

我想编辑这些术语并删除重复项以获得此结果:

 [1] "Science"  
 [2] "Science"  
 [3] "Arts & Humanities"  
 [4] "Arts & Humanities; Social Sciences"  
 [5] "Science"  
 [6] "Social Sciences; Science"  
 [7] "Science"  
 [8] "Social Sciences"  
 [9] "Social Sciences"  
[10] "Science"  
[11] "Science"  
[12] "Social Sciences; Science"  

到目前为止我只得到了这个:

stringedit <- function(A)  
{  
  A <-gsub("Biology", "Science", A)  
  A <-gsub("Cell Biology", "Science", A)  
  A <-gsub("Art", "Arts & Humanities", A)  
  A <-gsub("Humanities, Multidisciplinary", "Arts & Humanities", A)  
  A <-gsub("Psychology, Experimental", "Social Sciences", A)  
  A <-gsub("Astronomy & Astrophysics", "Science", A)  
  A <-gsub("Physics, Particles & Fields", "Science", A)  
  A <-gsub("Economics", "Social Sciences", A)  
  A <-gsub("Mathematics", "Science", A)  
  A <-gsub("Mathematics, Applied", "Science", A)  
  A <-gsub("Mathematics, Interdisciplinary Applications", "Science", A)  
  A <-gsub("Social Sciences, Mathematical Methods", "Social Sciences", A)  
  A <-gsub("Geriatrics & Gerontology", "Science", A)  
  A <-gsub("Gerontology", "Social Sciences", A)  
  A <-gsub("Management", "Social Sciences", A)  
  A <-gsub("Operations Research & Management Science", "Science", A)  
  A <-gsub("Computer Science, Artificial Intelligence", "Science", A)  
  A <-gsub("Computer Science, Information Systems", "Science", A)  
  A <-gsub("Engineering, Electrical & Electronic", "Science", A)  
  A <-gsub("Statistics & Probability", "Science", A)  
}  
B <- lapply(A, stringedit)  

但它无法正常工作:

> B  
[[1]]  
 [1] "Science"  
 [2] "Cell Science"  
 [3] "Arts & Humanities"  
 [4] "Arts & Humanities; Social Sciences"  
 [5] "Science; Science"  
 [6] "Social Sciences; Science, Interdisciplinary Applications; Social Sciences"  
 [7] "Science"  
 [8] "Social Sciences"  
 [9] "Social Sciences"  
[10] "Operations Research & Social Sciences Science"  
[11] "Computer Science, Arts & Humanitiesificial Intelligence; Science; Science"  
[12] "Social Sciences; Science, Interdisciplinary Applications; Social Sciences; Science"  

如何实现上述正确的输出？
非常感谢您提前考虑!

Answer 1

我发现将两列data.frame作为查找最简单,其中一列用于课程名称,一列用于该类别.这是一个例子:

course.categories <- data.frame(
  Course = 
  c("Art", "Humanities, Multidisciplinary", "Biology", "Cell Biology", 
    "Astronomy & Astrophysics", "Physics, Particles & Fields", "Mathematics", 
    "Mathematics, Applied", "Mathematics, Interdisciplinary Applications", 
    "Geriatrics & Gerontology", "Operations Research & Management Science", 
    "Computer Science, Artificial Intelligence", 
    "Computer Science, Information Systems", 
    "Engineering, Electrical & Electronic", "Statistics & Probability", 
    "Psychology, Experimental", "Economics", 
    "Social Sciences, Mathematical Methods", 
    "Gerontology", "Management"),
  Category =
  c("Arts & Humanities", "Arts & Humanities", "Science", "Science", 
    "Science", "Science", "Science", "Science", "Science", "Science", 
    "Science", "Science", "Science", "Science", "Science", "Social Sciences", 
    "Social Sciences", "Social Sciences", "Social Sciences", "Social Sciences"))

然后,假设A作为您问题中的列表:

sapply(strsplit(unlist(A), "; "), 
       function(x) 
         paste(unique(course.categories[match(x, course.categories[["Course"]]),
                                        "Category"]), 
               collapse = "; "))
#  [1] "Science"                            "Science"                           
#  [3] "Arts & Humanities"                  "Arts & Humanities; Social Sciences"
#  [5] "Science"                            "Social Sciences; Science"          
#  [7] "Science"                            "Social Sciences"                   
#  [9] "Social Sciences"                    "Science"                           
# [11] "Science"                            "Social Sciences; Science"

match将值A与course.categories数据集中的课程名称相匹配,并说明匹配发生在哪些行; 这用于提取课程所属的类别.然后,unique确保我们只有每个类别中的一个.paste把事情重新组合在一起

Answer 2

让我从一个例子开始。您有一个字符串“Cell Biology”。第一个替换 ，A <-gsub("Biology", "Science", A)将其变成“细胞科学”。那么就没有被替换。

由于您不使用正则表达式，我宁愿使用一种散列来进行替换：

myhash <- c( "Science", "Science", "Arts & Humanities", "Arts & Humanities", "Social Sciences", 
  "Science", "Science", "Social Sciences", "Science", "Science", "Science", "Social Sciences", 
  "Science", "Social Sciences", "Social Sciences", "Science", "Science", "Science", "Science", 
  "Science" )

names( myhash ) <- c( "Biology", "Cell Biology", "Art", "Humanities, Multidisciplinary", 
  "Psychology, Experimental", "Astronomy & Astrophysics", "Physics, Particles & Fields", "Economics", 
  "Mathematics", "Mathematics, Applied", "Mathematics, Interdisciplinary Applications", 
  "Social Sciences, Mathematical Methods", "Geriatrics & Gerontology", "Gerontology", "Management",
   "Operations Research & Management Science", "Computer Science, Artificial Intelligence", 
  "Computer Science, Information Systems", "Engineering, Electrical & Electronic", 
  "Statistics & Probability" )

现在，给定一个诸如“Biology”之类的字符串，您可以快速查找您的类别：

myhash[ "Biology" ]

我不确定为什么你想使用列表而不是字符串向量，因此我将简化你的情况：

A <- c("Biology","Cell Biology","Art",
  "Humanities, Multidisciplinary; Psychology, Experimental",
  "Astronomy & Astrophysics; Physics, Particles & Fields",
  "Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods",
  "Geriatrics & Gerontology","Gerontology","Management","Operations Research & Management Science",
  "Computer Science, Artificial Intelligence; Computer Science, Information Systems; Engineering, Electrical & Electronic",
  "Economics; Mathematics, Interdisciplinary Applications; Social Sciences, Mathematical Methods; Statistics & Probability")

has 查找不适用于复合字符串（包含“;”）。您可以拆分它们，但是使用strsplit. 然后，您可以使用unique避免术语重复，并使用该paste函数将其重新组合在一起。

stringedit <- function( x ) { 
  # first, split into subterms
  a.all <- unlist( strsplit( x, "; *" ) ) ; 
  paste( unique( myhash[ a.all ] ), collapse= "; " ) 
}

unlist( lapply( A, stringedit  ) )

这是所需的结果：

[1] "Science"                            "Science"                            "Arts & Humanities"                  "Arts & Humanities; Social Sciences"
[5] "Science"                            "Social Sciences; Science"           "Science"                            "Social Sciences"                   
[9] "Social Sciences"                    "Science"                            "Science"                            "Social Sciences; Science" 

当然，你可以*apply像这样多次调用：

a.spl <- sapply( A, strsplit, "; *" )
a.spl <- sapply( a.spl, function( x ) myhash[ x ] )
unlist( sapply( a.spl, collapse, "; " )

这并不比之前的代码效率更高或更低。

是的，您可以使用正则表达式实现相同的目的，但首先，它会涉及无论如何分割字符串，然后使用正则表达式^Biology$来确保它们匹配“Biology”而不是“Cell Biology”等。除非您想要结构类似于“.* Biology”。最后，无论如何，你都必须删除重复项，在我看来，这一切都将是（i）不那么冗长（=更容易出错）和（ii）不值得付出努力。