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根据R中另一列中的值替换一列中第二次出现的字符串

find-occurrences string regex r

0

carozimm · 技术社区 · 8 年前

以下是一个示例数据帧:

a <- c("cat", "dog", "mouse")
b <- c("my cat is a tabby cat and is a friendly cat", "walk the dog", "the mouse is scared of the other mouse")
df <- data.frame(a,b)

我希望能够删除b列a列中第二次出现的值。

这是我想要的输出:

a      b
cat    my cat is a tabby and is a friendly cat
dog    walk the dog
mouse  the mouse is scared of the other

我尝试了gsub和一些stringr函数的不同组合,但我甚至无法删除第二个(仅第二个)出现在b列a列中的字符串 this 一个,但我不熟悉Perl,无法将其转换为R。

谢谢

4 回复 | 直到 8 年前

1

G5W 8 年前

构建正确的正则表达式需要一些工作。

P1 = paste(a, collapse="|")
PAT = paste0("((", P1, ").*?)(\\2)")

sub(PAT, "\\1", b, perl=TRUE)
[1] "my cat is a tabby  and is a friendly cat"
[2] "walk the dog"                            
[3] "the mouse is scared of the other "

2

1

carozimm 8 年前

实际上,我已经找到了另一个解决方案,虽然时间更长,但对于其他regex初学者来说可能更清楚:

library(stringr)
# Replace first instance of col a in col b with "INTERIM" 
df$b <- str_replace(b, a, "INTERIM")

# Now that the original first instance of col a is re-labeled to "INTERIM", I can again replace the first instance of col a in col b, this time with an empty string
df$b <- str_replace(df$b, a, "")

# And I can re-replace the re-labeled "INTERIM" to the original string in col a
df$b <- str_replace(df$b, "INTERIM", a)

# Trim "double" whitespace
df$b <- str_replace(gsub("\\s+", " ", str_trim(df$b)), "B", "b")


df
a            b
cat          my cat is a tabby and is a friendly cat
dog          walk the dog
mouse        the mouse is scared of the other

3

0

Andrew Gustar 8 年前

你可以这样做。。。

library(stringr)
df$b <- str_replace(df$b, 
                    paste0("(.*?",df$a,".*?) ",df$a), 
                    "\\1")

df
      a                                       b
1   cat my cat is a tabby and is a friendly cat
2   dog                            walk the dog
3 mouse        the mouse is scared of the other

正则表达式查找第一个字符串 df$a 在它的某个地方,然后是一个空间和另一个空间 df$年 。捕获组是第二次出现之前的空格内的文本(由 (...) ),并且整个文本(包括第二个匹配项)被捕获组替换 \\1 (具有删除第二个 df$年 以及它前面的空格)。第二次之后的任何事情 df$年 不受影响。

4

0

hello_friend 6 年前

基本R,拆分应用组合解决方案:

# Split-apply-combine: 

data.frame(do.call("rbind", lapply(split(df, df$a), function(x){

        b <- paste(unique(unlist(strsplit(x$b, "\\s+"))), collapse = " ")

        return(data.frame(a = x$a, b = b))

      }

    )

  ), 

  stringsAsFactors = FALSE, row.names = NULL

)

数据:

df <- data.frame(a = c("cat", "dog", "mouse"),
                 b = c("my cat is a tabby cat and is a friendly cat", "walk the dog", "the mouse is scared of the other mouse"), 
                 stringsAsFactors = FALSE)