How can I remove leading zeros for two digits number (01, 02, etc.) from the middle of character string using R?
For the following string vector s, I hope to remove leading zeros in each elements, which is reverse of the answer from this link:
s <- c('week 01st', 'weeks 02nd', 'year2022week01st', 'week 4th')
The expected result will like:
s <- c('week 1st', 'weeks 2nd', 'year2022week1st', 'week 4th')
I test the following code, it's not working out since the regex syntax is not complete:
s <- 'week 01st'
sub('^0+(?=[1-9])', '', s, perl=TRUE)
sub('^0+([1-9])', '\\1', s)
Out:
[1] "week 01st"
How could I do that using R?
Update: for the following code contributed by @dvantwisk, it works for year2022week01st, but not suitable to other elements:
s <- c('week 01st', 'weeks 02nd', 'year2022week01st', 'week 4th')
gsub('(year[0-9]{4,})(week)(0{0,})([1-9]{1})([0-9a-zA-Z]{1,})', '\\1\\2\\4\\5', s)
Out:
[1] "week 01st" "weeks 02nd" "year2022week1st" "week 4th"
Solution 1:
gsub('(week )(0{0,})([1-9]{1})([0-9a-zA-Z]{1,})', '\\1\\3\\4', week_string)
gsub() takes three arguments as input: a pattern, a replacement, and a query character vector. Our strategy is to create a regular expression with four groups with ()s.
We fist match 'week '.
We then match zero or more zeros with the expression (0{0,}). The first zero indicates the character we are trying to match and the expression {0,} indicates we are trying to match zero (hence the 0) or more (hence the comma) times.
Our third group is matching any number between 1 to 9 one time.
Out fourth group is to match any number between 0 to 9 or any letter 1 or more times
Our replacement is '\\1\\3\\4'. This indicates we only want to keep group one and three in our result. Thus the output is:
[1] "week 1st" "week 2nd" "week 3rd" "week 4th"
Solution 2:
You might use:
weeks?\h*\K0+(?=[1-9]\d*[a-zA-Z])
The pattern matches:
-
weeks?Match week with optional s -
\h*\KMatch optional spaces and forget what is matched so far -
0+Match 1+ times a zero -
(?=[1-9]\d*[a-zA-Z])Positive lookahead, assert a char 1-9, optional digit and a char a-zA-Z to the right
See a Regex demo and a R demo.
In the replacement use an empty string.
For example
s <- c('week 01st', 'weeks 02nd', 'year2022week01st', 'week 4th')
gsub("weeks?\\h*\\K0+(?=[1-9]\\d*[a-zA-Z])", '', s, perl=T)
Output
[1] "week 1st" "weeks 2nd" "year2022week1st" "week 4th"
Or with 2 capture groups:
(weeks?\h*)0+([1-9]\d*[a-zA-Z])
Example:
s <- c('week 01st', 'weeks 02nd', 'year2022week01st', 'week 4th')
gsub("(weeks?\\h*)0+([1-9]\\d*[a-zA-Z])", '\\1\\2', s,)
Output
[1] "week 01st" "weeks 02nd" "year2022week1st" "week 4th"