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

[Duncan Murdoch]

On 17/09/2015 5:11 PM, Dimitri Liakhovitski wrote:
> (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)]

Your verbal description doesn't match your regexp, and you didn't show
us your output, so how can we tell whether this is you not understanding
regular expressions, or an actual problem?

When I try this example, I get

character(0)

which is the correct outcome, given the input string.

Duncan Murdoch

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