Renaming vectors in a column - r

Question

I have a dataframe which, summarised, looks like this:
CEMETERY SEX CONTEXT RaHD.L RaHD.R
1 Medieval-St. Mary Graces FEMALE 7172 21.2 21.6
2 Medieval-St. Mary Graces MALE 6225 23.9 25.2
3 Medieval-St. Mary Graces MALE 9987 23.9 23.5
4 Medieval-St. Mary Graces MALE 11475 22.4 22.3
5 Medieval-St. Mary Graces MALE 12356 25.8 25.4
6 Medieval-St. Mary Graces MALE 12525 22.4 22.3
7 Medieval-St. Mary Graces MALE 12785 22.9 22.6
8 Medieval-St. Mary Graces MALE 13840 22.5 22.9
9 Medieval-Spital Square FEMALE 383 21.5 22.0
10 Medieval-Spital Square MALE 31 23.3 22.0
17 Post-Medieval-Chelsea Old Church FEMALE 19 20.0 20.6
18 Post-Medieval-Chelsea Old Church FEMALE 31 19.5 20.0
19 Post-Medieval-Chelsea Old Church FEMALE 39 19.6 19.2
41 Post-Medieval-St. Thomas Hospital FEMALE 60 21.8 22.6
43 Post-Medieval-St. Thomas Hospital MALE 83 22.4 23.0
I want to change the vectors in the CEMETERY column to simply 'Medieval' and 'Post-Medieval', instead of having the entire cemetery name, or alternatively create a new column stating 'Medieval' or 'Post-medieval'.

Answer 1

We can use sub to capture the substring upto "Medieval" and then in the replacement use the backreference (\\1) for the captured substring
df1$CEMETERY <- sub("(.*(M|m)edieval).*", "\\1", df1$CEMETERY)
df1$CEMETERY
#[1] "Medieval" "Medieval" "Medieval" "Medieval"
#[5] "Medieval" "Medieval" "Medieval" "Medieval"
#[9] "Medieval" "Medieval" "Post-Medieval" "Post-Medieval"
#[13] "Post-Medieval" "Post-Medieval" "Post-Medieval"

Answer 2

In case the information on the location should be kept, there is an alternative approach which splits the CEMETERY column at the first hyphen after "Medieval" (which includes splitting after "Post-Medieval") and assigns the two parts to two columns PERIOD and CEMETERY:
library(data.table)
setDT(DF)[, c("PERIOD", "CEMETERY") := tstrsplit(CEMETERY, "(?<=Medieval)-", perl = TRUE)][]
CEMETERY SEX CONTEXT RaHD.L RaHD.R PERIOD
1: St. Mary Graces FEMALE 7172 21.2 21.6 Medieval
2: St. Mary Graces MALE 6225 23.9 25.2 Medieval
3: St. Mary Graces MALE 9987 23.9 23.5 Medieval
4: St. Mary Graces MALE 11475 22.4 22.3 Medieval
5: St. Mary Graces MALE 12356 25.8 25.4 Medieval
6: St. Mary Graces MALE 12525 22.4 22.3 Medieval
7: St. Mary Graces MALE 12785 22.9 22.6 Medieval
8: St. Mary Graces MALE 13840 22.5 22.9 Medieval
9: Spital Square FEMALE 383 21.5 22.0 Medieval
10: Spital Square MALE 31 23.3 22.0 Medieval
11: Chelsea Old Church FEMALE 19 20.0 20.6 Post-Medieval
12: Chelsea Old Church FEMALE 31 19.5 20.0 Post-Medieval
13: Chelsea Old Church FEMALE 39 19.6 19.2 Post-Medieval
14: St. Thomas Hospital FEMALE 60 21.8 22.6 Post-Medieval
15: St. Thomas Hospital MALE 83 22.4 23.0 Post-Medieval
The feature used in the regular expression to identify the correct hyphen to split on is called positive look-behind.
Data
DF <- readr::read_table(
" CEMETERY SEX CONTEXT RaHD.L RaHD.R
1 Medieval-St. Mary Graces FEMALE 7172 21.2 21.6
2 Medieval-St. Mary Graces MALE 6225 23.9 25.2
3 Medieval-St. Mary Graces MALE 9987 23.9 23.5
4 Medieval-St. Mary Graces MALE 11475 22.4 22.3
5 Medieval-St. Mary Graces MALE 12356 25.8 25.4
6 Medieval-St. Mary Graces MALE 12525 22.4 22.3
7 Medieval-St. Mary Graces MALE 12785 22.9 22.6
8 Medieval-St. Mary Graces MALE 13840 22.5 22.9
9 Medieval-Spital Square FEMALE 383 21.5 22.0
10 Medieval-Spital Square MALE 31 23.3 22.0
17 Post-Medieval-Chelsea Old Church FEMALE 19 20.0 20.6
18 Post-Medieval-Chelsea Old Church FEMALE 31 19.5 20.0
19 Post-Medieval-Chelsea Old Church FEMALE 39 19.6 19.2
41 Post-Medieval-St. Thomas Hospital FEMALE 60 21.8 22.6
43 Post-Medieval-St. Thomas Hospital MALE 83 22.4 23.0"
)[, -1]