Find first occurrence of a character in column of a data frame in R

Struggling with string handling in R...

I've got a column of strings in an R data frame. Each one contains the "=" character once and only once. I'd like to know the position of the "=" character in each element of the column, as a step to splitting the column into two separate columns (one for the bit before the "=" and one for the bit after the "="). Can anyone help please? I'm sure it's simple but I'm struggling to find the answer.

For example, if I have:

x <- data.frame(string = c("aa=1", "aa=2", "aa=3", "b=1", "b=2", "abc=5"))

I'd like a bit of code to return

> (3, 3, 3, 2, 2, 4)

Thank you.

Here's a way to do:

library(stringr)
str_locate(x$string, "=")[,1]

In Base R you can do:

as.numeric(lapply(strsplit(as.character(x$string), ""), function(x) which(x == "=")))

>[1] 3 3 3 2 2 4

You can use gregexpr:

unlist(lapply(gregexpr(pattern = '=', x$string), min))
[1] 3 3 3 2 2 4

To get the position of "=" you can use the regexp function:

regexpr("=", x$string)
#[1] 3 3 3 2 2 4
#attr(,"match.length")
#[1] 1 1 1 1 1 1
#attr(,"useBytes")
#[1] TRUE 

However, as @Michael stated if your goal is to split the string you can use strsplit:

strsplit(x$string, "=")
#[[1]]
#[1] "aa" "1" 
#
#[[2]]
#[1] "aa" "2" 
#
#[[3]]
#[1] "aa" "3" 
#
#[[4]]
#[1] "b" "1"
#
#[[5]]
#[1] "b" "2"
#
#[[6]]
#[1] "abc" "5"

Or to combine with do.call and `rbind to create a new dataframe:

do.call(rbind, strsplit(x$string, "="))
#     [,1]  [,2]
#[1,] "aa"  "1" 
#[2,] "aa"  "2" 
#[3,] "aa"  "3" 
#[4,] "b"   "1" 
#[5,] "b"   "2" 
#[6,] "abc" "5" 

Here is another solution to obtain a two column dataframe, the first containing the characters before = and the second one containing the characters after =. You can do that without obtaining the positions of the = character.

library(stringr)

t(as.data.frame(strsplit(x$string, "=")))

#              [,1]  [,2]
#c..aa....1..  "aa"  "1" 
#c..aa....2..  "aa"  "2" 
#c..aa....3..  "aa"  "3" 
#c..b....1..   "b"   "1" 
#c..b....2..   "b"   "2" 
#c..abc....5.. "abc" "5"

Some may find this more readable

library(tidyverse)
x %>%
  mutate(
    number = string %>% str_extract('[:digit:]+'),
    text = string %>%  str_extract('[:alpha:]+')
  ) %>%
  as_tibble()
# A tibble: 6 x 3
  string number text 
  <fct>  <chr>  <chr>
1 aa=1   1      aa   
2 aa=2   2      aa   
3 aa=3   3      aa   
4 b=1    1      b    
5 b=2    2      b    
6 abc=5  5      abc