R: grep, what am I doing wrong?

Question

I want to get all the positions of "_" in my string:

MyString <- "Test_Test_Test"

grep("_", MyString)

This returns however:

[1] 1

What am I doing wrong?

Answer 1

Use gregexpr rather than grep

 MyString<-"Test_Test_Test"
> gregexpr('_', MyString)
[[1]]
[1]  5 10
attr(,"match.length")
[1] 1 1
attr(,"useBytes")
[1] TRUE

Answer 2

I'd recommend Hadley's stringr package:

library("stringr")

MyString <- "Test_Test_Test"
str_locate_all(MyString, "_")
# [[1]]
#  start end
# [1,]     5   5
# [2,]    10  10