CODEWITHSUNDEEP
regexr
seaotternerd
seaotternerd

Reputation: 6419

Retrieve digits after specific string in R

I have a bunch of strings that contain the word "radius" followed by one or two digits. They also contain a lot of other letters, digits, and underscores. For example, one is "inflow100_radius6_distance12". I want a regex that will just return the one or two digits following "radius." If R recognized \K, then I would just use this:

radius\K[0-9]{1,2}

and be done. But R doesn't allow \K, so I ended up with this instead (which selects radius and the following numbers, and then cuts off "radius"):

result <- regmatches(input_string, gregexpr("radius[0-9]{1,2}", input_string))
result <- unlist(substr(result, 7, 8)))

I'm pretty new to regex, so I'm sure there's a better way. Any ideas?

Upvotes: 5

Views: 797

Answers (2)

hwnd
hwnd

Reputation: 70750

\K is recognized. You can solve the problem by turning on the perl = TRUE parameter.

result <- regmatches(x, gregexpr('radius\\K\\d+', x, perl=T))

Upvotes: 8

G. Grothendieck
G. Grothendieck

Reputation: 270378

1) Match the entire string replacing it with the digits after radius:

sub(".*radius(\\d+).*", "\\1", "inflow100_radius6_distance12")
## [1] "6"

The regular expression can be visualized as follows:

.*radius(\d+).*

Regular expression visualization

Debuggex Demo

2) This also works, involves a simpler regular expression and converts it to numeric at the same time:

library(gsubfn)
strapply("inflow100_radius6_distance12", "radius(\\d+)", as.numeric, simplify = TRUE)
## [1] 6

Here is a visualization of the regular expression:

radius(\d+)

Regular expression visualization

Debuggex Demo

Upvotes: 4

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