提取字符串中的前2个字符

Question

我需要提取字符串中的前2个字符以便稍后创建bin图分布.向量:

x <- c("75 to 79", "80 to 84", "85 to 89") 

我已经走到这一步了:

substrRight <- function(x, n){
  substr(x, nchar(x)-n, nchar(x))
}

调用功能

substrRight(x, 1)

响应

[1] "79" "84" "89"

需要打印最后2个字符而不是第一个字符.

[1] "75" "80" "85"

Answer 1

您可以直接使用该substr函数来获取每个字符串的前两个字符:

x <- c("75 to 79", "80 to 84", "85 to 89")
substr(x, start = 1, stop = 2)
# [1] "75" "80" "85"

您还可以编写一个简单的函数来执行"反向"子字符串,假设索引从字符串的末尾开始,给出'start'和'stop'值:

revSubstr <- function(x, start, stop) {
  x <- strsplit(x, "")
  sapply(x, 
         function(x) paste(rev(rev(x)[start:stop]), collapse = ""), 
         USE.NAMES = FALSE)
}
revSubstr(x, start = 1, stop = 2)
# [1] "79" "84" "89" 

Answer 2

这是一个stringr解决方案：

str_extract(x, "^.{3}")

Answer 3

使用gsub...

x <- c("75 to 79", "80 to 84", "85 to 89") 

gsub(" .*$", "", x) # Replace the rest of the string after 1st space with  nothing
[1] "75" "80" "85"