R-使用正则表达式和ifelse条件从字符串中分离文本时出错

Question

What I want to do is to strip text from a string where ever there is an ":".

Suppose my text contains:

 text$Text[[3]] = "There is a horror movie running in the iNox theater. : Can we go?"

And what I want to create a dataframe such that:

  Col1                                                    Col2
  There is a horror movie running in the iNox theater.    Can we go?

I am trying to use the following :

 df = data.frame(Text = strsplit(text$Text[[3]], 
                 ifelse(":", ":", text$Text[[3]]))[[1]], stringsAsFactors = F)

dat3$Text[[3]] because the text is in row no. 3 of the text$Text.

But the above ifelse() logic did not work. Here I was trying to use ifelse condition such that if there is a ":" in the text, use ":" otherwise use the complete text as it is. So it means in case if there is no ":" then the result would look like something:

 text$Text[[3]] = "Hi Mom, You there. Can I go to Jimmy's house?"

 Col1                                                 Col2
 Hi Mom, You there. Can I go to Jimmy's house?         NA

How to do it correctly?

Please note that there is a catch:

• What if there are two ":" in the text??
• I would like to consider only that ":" which is within first two lines and not in the rest of the text?

Answer 1

I find the following too complicated, someone with more knowledge than me on regular expressions will surely come up with a better solution.

test <- c(
"There is a horror movie running in the iNox theater. : Can we go?",
"Hi Mom, You there. Can I go to Jimmy's house?",
"Hi : How are you : Lets go")

fun <- function(x, pattern = ":"){
    re <- regexpr(pattern, x)
    res <- sapply(seq_along(re), function(i){
        if(re[i] > 0){
            Col1 <- trimws(substring(x[i], 1, re[i] - 1))
            Col2 <- trimws(substring(x[i], re[i] + 1))
        } else {
            Col1 <- x[i]
            Col2 <- NA
        }
        c(Col1 = Col1, Col2 = Col2)
    })
    as.data.frame(t(res))
}

fun(test)

Answer 2

You don't really need an if else statement for this. Regex is built to handle conditions like this.

For the first case of data with just one symbol – a colon (":") in this example – we can use this:

x <- "There is a horror movie running in the iNox theater. : Can we go?"

data.frame(Col1=gsub("(.*)+\\s[:]\\s+(.*)","\\1",x), 
           Col2=gsub("(.*)+\\s[:]\\s+(.*)","\\2",x))

Output:

                                                  Col1            Col2
1 There is a horror movie running in the iNox theater.      Can we go?

Now let's say you have more than one symbol in your string and you want to be able to keep information before the first symbol in the first column, and information after the first symbol in the second column. To do this, try using the "?" regex symbol, like this:

x <- "There is a horror movie running in the iNox theater. : Can we go? : Please?"

data.frame(Col1=gsub("\\s\\:.*$","\\1",x), 
           Col2=gsub("^[^:]+(?:).\\s","\\1",x))

Output:

                                                  Col1                      Col2
1 There is a horror movie running in the iNox theater.      Can we go? : Please?

For more information on using regex symbols in R, this is a helpful reference .

Answer 3

test <- "There is a horror movie running in the iNox theater. : Can we go?"
df = data.frame(Col1 = strsplit(test,":")[[1]][1],
                Col2 = strsplit(test,":")[[1]][2],
                stringsAsFactors = F)
df
#                                                   Col1        Col2
#1 There is a horror movie running in the iNox theater.   Can we go?

Notice that the unusual first line of strsplit()'s output consists of [[1]]. Similar to the way that R displays vectors, [[1]] means that R is showing the first element of a list.

Answer 4

You can use the package stringr

library(stringr) 
str_split_fixed("HI : How are you : Lets go", ":", 3)

In the above function str_split_fixed "Hi : How are you : Lets go" is the sentence or string you want to use and ":" is the seperator in the string , and 3 is the number of columns you want the string to be split into

In your case last value should be 2 , as you want to split into 2 columns