16

I would like to capitalize everything in a character vector that comes after the first _. For example the following vector:

x <- c("NYC_23df", "BOS_3_rb", "mgh_3_3_f")

Should come out like this:

"NYC_23DF" "BOS_3_RB" "mgh_3_3_F"

I have been trying to play with regular expressions, but am not able to do this. Any suggestions would be appreciated.

Mikko
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  • `gsub("(\\_*)", "", x)` picks `_`, but doesn't pick the rest of the string. There are good examples on capitalization in the help sheet. – Mikko May 29 '12 at 08:30

3 Answers3

26

You were very close:

gsub("(_.*)","\\U\\1",x,perl=TRUE)

seems to work. You just needed to use _.* (underscore followed by zero or more other characters) rather than _* (zero or more underscores) ...

To take this apart a bit more:

  • _.* gives a regular expression pattern that matches an underscore _ followed by any number (including 0) of additional characters; . denotes "any character" and * denotes "zero or more repeats of the previous element"
  • surrounding this regular expression with parentheses () denotes that it is a pattern we want to store
  • \\1 in the replacement string says "insert the contents of the first matched pattern", i.e. whatever matched _.*
  • \\U, in conjunction with perl=TRUE, says "put what follows in upper case" (uppercasing _ has no effect; if we wanted to capitalize everything after (for example) a lower-case g, we would need to exclude the g from the stored pattern and include it in the replacement pattern: gsub("g(.*)","g\\U\\1",x,perl=TRUE))

For more details, search for "replacement" and "capitalizing" in ?gsub (and ?regexp for general information about regular expressions)

Ben Bolker
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  • +1 for the `"\\U\\1"`. Never seen that kind of regex before in R. Could you explain what this does in particular and/or where to look it up? I assume `"\\U"` handles the uppercase, but I don't really get the `"\\1"`. Thanks! – Rappster May 29 '12 at 09:03
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    The `\\1` is a back-reference to the first matched pattern. It's all in the examples for `?gsub`, which is where I looked ... – Ben Bolker May 29 '12 at 09:14
  • As so often when working with R: the answer is so simple, only if you know what you're doing =D. Thanks Ben Bolker! – Mikko May 29 '12 at 09:32
  • I love regex solutions like this; simple. +1 I myself have benefited from regex solutions like this, especially, when the poster adds info about what each piece is doing. Ben if it's not too much trouble could you add a slight bit of explanation about what each piece is doing for future thread searchers? – Tyler Rinker May 29 '12 at 17:50
14

gsubfn in the gsubfn package is like gsub except the replacement string can be a function. Here we match _ and everything afterwards feeding the match through toupper :

library(gsubfn)

gsubfn("_.*", toupper, x)
## [1] "NYC_23DF"  "BOS_3_RB"  "mgh_3_3_F"

Note that this approach involves a particularly simple regular expression.

G. Grothendieck
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4

Simple example using base::strsplit

x <- c("NYC_23df", "BOS_3_rb", "mgh_3_3_f", "a") 

myCap <- function(x) {
    out <- sapply(x, function(y) {
        temp <- unlist(strsplit(y, "_"))
        out <- temp[1]
        if (length(temp[-1])) {
            out <- paste(temp[1], paste(toupper(temp[-1]), 
                collapse="_"), sep="_") 
        }
        return(out)
    })
    out
}

> myCap(x)
   NYC_23df    BOS_3_rb   mgh_3_3_f           a 
 "NYC_23DF"  "BOS_3_RB" "mgh_3_3_F"         "a"

Example using the stringr package

pkg <- "stringr"
if (!require(pkg, character.only=TRUE)) {
    install.packages(pkg)
    require(pkg, character.only=TRUE)   
}

myCap.2 <- function(x) {
    out <- sapply(x, function(y) {
        idx <- str_locate(y, "_")
        if (!all(is.na(idx[1,]))) {
            str_sub(y, idx[,1], nchar(y)) <- toupper(str_sub(y, idx[,1], nchar(y))) 
        }
        return(y)
    })
    out
}

> myCap.2(x)
   NYC_23df    BOS_3_rb   mgh_3_3_f           a 
 "NYC_23DF"  "BOS_3_RB" "mgh_3_3_F"         "a"
Rappster
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