selecting rows in a data.frame in which a certain column has values containing one of a set of prefixes

Question

I have a data.frame of the type:

> head(engschools)
RECTYPE LEA ESTAB    URN                        SCHNAME               TOWN    PCODE       
1       1 919  2028 138231              Alban City School          n.a.       E1 3RR 
2       1 919  4003 138582           Samuel Ryder Academy          St Albans  AL1 5AR 
3       1 919  2004 138201 Hatfield Community Free School           Hatfield  AL10 8ES 
4       2 919  7012 117671               St Luke's School          n.a        BR3 7ET 
5       1 919  2018 138561          Harpenden Free School           Redbourn  AL3 7QA 
6       2 919  7023 117680                Lakeside School Welwyn Garden City  AL8 6YN 

And a set of prefixes like this one:

>head(prefixes)
E
AL

I would like to select the rows from the data.frame engschools that have values in column PCODE which contain one of the prefixes in prefixes . The correct result would thus contain rows 1:3 and 5:6 but not row 4 .

Answer 1

You can try something like this:

mydf[grep(paste0("^", prefixes, collapse="|"), engschools$PCODE), ]
#   RECTYPE LEA ESTAB    URN                        SCHNAME               TOWN    PCODE
# 1       1 919  2028 138231              Alban City School               n.a.   E1 3RR
# 2       1 919  4003 138582           Samuel Ryder Academy          St Albans  AL1 5AR
# 3       1 919  2004 138201 Hatfield Community Free School           Hatfield AL10 8ES
# 5       1 919  2018 138561          Harpenden Free School           Redbourn  AL3 7QA
# 6       2 919  7023 117680                Lakeside School Welwyn Garden City  AL8 6YN

Here, we have used:

• paste to create our search pattern (in this case, "^E|^AL" ).
• grep to identify the row indexes that match the provided pattern.
• Basic [ style extracting to extract the relevant rows.