[R] Hep with regex! - combination of ^, |, \\, _ and $

[Dimitri Liakhovitski]

(x <- c("q10_1", "q10_2", "q10_11", "q12_1", "q12_2", "q13_1", "q13_11"))

# Which strings start with "q10" or "q12? - WORKS
x[grep("^q10|q12", x)]

# Which strings end with "1"? - WORKS
x[grep("1$", x)]

# Which strings end with "_1"? - WORKS
x[grep("\\_1$", x)]

# Which strings start with "q10" AND contain a "1"? - WORKS
x[grep("^q10.+1", x)]

# Which strings start with "q10" AND end with a "_1"? - DOES NOT WORK
x[grep("^q10.+\\_1$", x)]

# Which strings start with "q10" or "q12 AND end with "_1"? - WORKS INCORRECTLY
x[grep("^q10|q12.+\\_1$", x)]

Thank you!
Dimitri Liakhovitski