Add a character to the start of every word

Question

I have a vector of strings and want to add a + before each word in each string.

strings <- c('string one', 'string two', 'string three')
strings_new <- str_replace_all(strings, "\\b\\w", '+')
string_new

Unfortunately, this is replacing the first character, not adding the + symbol. I'm not too familiar with regex to know how to solve this.

Any help would be great.

Thanks

Answer 1

Using captured groups is one way of doing this. Group with parenthesis and recall with \\1.

strings_new <- str_replace_all(strings, "(\\b\\w)", '+\\1')
strings_new
[1] "+string +one"   "+string +two"   "+string +three"

Answer 2

You may use a base R solution using PCRE regex [[:<:]] that matches the starting word boundary, a location between a non-word and a word char:

strings <- c('string one', 'string two', 'string three')
gsub("[[:<:]]", "+", strings, perl=TRUE)
# => [1] "+string +one"   "+string +two"   "+string +three"

Or, you may use a (\w+) (that matches and captures into Group 1 any one or more word chars, i.e. letters, digits, or _) TRE regex to replace with a + and a replacement backreference \1 to restore the consumed chars in the output:

gsub("(\\w+)", '+\\1', strings)
# => [1] "+string +one"   "+string +two"   "+string +three"

Note you do not need a word boundary here since the first word char matched will be already at the word boundary and the consequent word chars will be consumed due to + quantifier. See the regex demo.

And with an ICU regex based str_replace_all, you may use

> str_replace_all(strings, "\\w+", '+\\0')
[1] "+string +one"   "+string +two"   "+string +three"

The \\0 is a replacement backreference to the whole match.