如何从 R 中的日期列中提取月份？

Question

I need to create a dataframe column in R that contains month and year for the observation (in this case, publications from the Web of Science database). I have tried concatenating the current columns "PD" (publication date) and "PY" (publication year). However, the column "PD" uses two formats: abbreviated month alone (eg "MAR") and day-abbreviated month (eg "12-Mar"). I would like the new "date" column to have a uniform format of "abbreviated-month year" (eg "MAR 2020") so that I can statistically analyze it.

How do I extract the month from the "PD" column (ie "MAR" instead of "12-Mar")?

Answer 1

We can use sub

 toupper(sub("[0-9 -]+", "", df1$PD))
 #[1] "MAR"  "MAR"  "JUNE" "JUNE"

data

df1 <- data.frame(PD = c("MAR", "12-Mar", "JUNE", "24-June"), 
       stringsAsFactors= FALSE)

Answer 2

We can extract only alphabets from PD column.

toupper(stringr::str_extract(df$PD, '[A-Za-z]+'))
#[1] "MAR"   "MAY"   "APRIL" "JUNE" 

data

df <- data.frame(PD = c("MAR", "13-May", "April", "24-June"), 
                 stringsAsFactors= FALSE)