You could do this:
df <- data.frame(date=c("18MAY2013:00:00:00","19MAY2013:00:00:00"))
df$year <- format(as.Date(df$date,"%d%B%Y"),"%Y")
df$month <- format(as.Date(df$date,"%d%B%Y"),"%m")
date year month
1 18MAY2013:00:00:00 2013 05
2 19MAY2013:00:00:00 2013 05
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solved How can I create a new column for month and year from datetime and logically compare date time in R [closed]