CODEWITHSUNDEEP
rregexgrepl
user11538509
user11538509

Reputation:

regex in R: Number range after letter at end of string

I have column names that are something like this:

colnames <- c("a81", "b82", "a181", "b182")

I want to extract only columns that have either 81 or 82 at the end and before those numbers (81 and 82) there should be a letter. I want to use regex in grepl and the expected output here is

TRUE TRUE FALSE FALSE

What I tried so far is

grepl("[:alpha:][81-82]$", colnames)

Unfortunately, the code returns FALSE for all entries. What am I doing wrong?

Upvotes: 0

Views: 648

Answers (2)

J_Alaniz
J_Alaniz

Reputation: 98

I'd go with

grepl("[a-z](81|82)$", colnames)

[a-z] means any letter and the parentheses group any of the next 2 characters: i.e. either 81 OR (|) 82.

Upvotes: 2

akrun
akrun

Reputation: 887971

The [:alpha:] needs to be changed to [[:alpha:]] and instead of [81-82], it can be 8 followed by [1-2]

grepl("^[[:alpha:]]8[1-2]$", colnames)
#[1]  TRUE  TRUE FALSE FALSE

Or we can specify

grepl("^[A-Za-z]8[1-2]$", colnames)

Upvotes: 1

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