查找字符串中字符的位置

I would like to find the location of a character in a string.

我想找到字符串中字符的位置。

Say: string = "the2quickbrownfoxeswere2tired"

说:字符串= " the2quickbrownfoxeswere2tired "

I would like the function to return 4 and 24 -- the character location of the 2s in string.

我希望函数返回4和24——字符串中2s的字符位置。

4 个解决方案

#1

You can use gregexpr

您可以使用gregexpr

 gregexpr(pattern ='2',"the2quickbrownfoxeswere2tired")


[[1]]
[1]  4 24
attr(,"match.length")
[1] 1 1
attr(,"useBytes")
[1] TRUE

or perhaps str_locate_all from package stringr which is a wrapper for ~~gregexpr~~ stringi::stri_locate_all (as of stringr version 1.0)

或者str_locate_all来自于stringr包这是gregexpr stringi::stri_locate_all的包装(从stringr版本1.0开始)

library(stringr)
str_locate_all(pattern ='2', "the2quickbrownfoxeswere2tired")

[[1]]
     start end
[1,]     4   4
[2,]    24  24

note that you could simply use stringi

注意，您可以使用stringi

library(stringi)
stri_locate_all(pattern = '2', "the2quickbrownfoxeswere2tired", fixed = TRUE)

Another option in base R would be something like

另一个以R为底的选项是类似的

lapply(strsplit(x, ''), function(x) which(x == '2'))

should work (given a character vector x)

应该可以工作(给定字符向量x)

#2

Here's another straightforward alternative.

这是另一个简单的选择。

> which(strsplit(string, "")[[1]]=="2")
[1]  4 24

#3

You can make the output just 4 and 24 using unlist:

可以使用unlist使输出仅为4和24:

unlist(gregexpr(pattern ='2',"the2quickbrownfoxeswere2tired"))
[1]  4 24

#4

find the position of the nth occurrence of str2 in str1(same order of parameters as Oracle SQL INSTR), returns 0 if not found

查找str1中第n次出现str2的位置(与Oracle SQL INSTR的参数顺序相同)，如果没有找到则返回0

instr <- function(str1,str2,startpos=1,n=1){
    aa=unlist(strsplit(substring(str1,startpos),str2))
    if(length(aa) < n+1 ) return(0);
    return(sum(nchar(aa[1:n])) + startpos+(n-1)*nchar(str2) )
}


instr('xxabcdefabdddfabx','ab')
[1] 3
instr('xxabcdefabdddfabx','ab',1,3)
[1] 15
instr('xxabcdefabdddfabx','xx',2,1)
[1] 0

#1