CODEWITHSUNDEEP
rregex
MortenAnthonsen
MortenAnthonsen

Reputation: 78

regex single digit

I have a question which I think is solved by regex use in R.

I have a set of dates (as chr) which I would like in a different format (as chr).

I have tried to fool around with the below examples where the first (new_dates) gives the right format for months 1-9 and wrong for 10-12 and (new_dates2) gives the right format for 10-12 but nothing for 1-9.

I see that the code in the first case matches a single digit twice for 10-12, but don't really know how to tell it to match only single digit.

The final vector of correct dates shows the result I would like. 

dates <- c("1/2016", "2/2016", "3/2016", "4/2016", "5/2016", "6/2016", "7/2016", "8/2016", "9/2016", "10/2016", "11/2016", "12/2016", "1/2017")
new_dates <- sub("(\\d)[:/:](\\d{4})","\\2M0\\1", dates)
new_dates2 <- sub("(\\d{2})[:/:](\\d{4})","\\2M\\1", dates)
correctdates <- c("2016M01", "2016M02", "2016M03", "2016M04", "2016M05", "2016M06", "2016M07", "2016M08", "2016M09", "2016M10", "2016M11", "2016M12", "2017M1")

Upvotes: 1

Views: 370

Answers (3)

lmo
lmo

Reputation: 38500

Here's a base R method that will return the desired format: 

format(as.Date(paste0("1/",dates), "%d/%m/%Y"), "%YM%m")
[1] "2016M01" "2016M02" "2016M03" "2016M04" "2016M05" "2016M06" "2016M07" "2016M08" "2016M09"
[10] "2016M10" "2016M11" "2016M12" "2017M01"

The idea is to first convert to a Date object and then use the format function to create the desired character representation. I pasted on 1/ so that a day is present in each element.

Upvotes: 1

Liun
Liun

Reputation: 117

new_dates <- sub("(\\d{1,2})\\/(\\d{4})","\\2M0\\1", dates)

It's fine.

Upvotes: 0

jjspace
jjspace

Reputation: 187

As @a p o m said it might be better to look for another solution if you are manipulating dates but if you want to stick with regular expressions you can try this one.

([02-9]|1[0-2]?)[:\/](\d{4}) example

Upvotes: 0

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