r - grep using a character vector with multiple patterns -


i trying use grep test whether vector of strings present in vector or not, , output values present (the matching patterns).

i have data frame this:

firstname letter    alex      a1 alex      a6 alex      a7 bob       a1 chris     a9 chris     a6

i have vector of strings patterns found in "letter" columns, example: c("a1", "a9", "a6").

i check whether of strings in pattern vector present in "letter" column. if are, output of unique values.

the problem is, don't know how use grep multiple patterns. tried:

matches <- unique (     grep("a1| a9 | a6", myfile$letter, value=true, fixed=true) )

but gives me 0 matches not true, suggestions?

in addition @marek's comment not including fixed==true, need not have spaces in regular expression. should "a1|a9|a6".

you mention there lots of patterns. assuming in vector

tomatch <- c("a1", "a9", "a6")

then can create regular expression directly this.

matches <- unique (grep(paste(tomatch,collapse="|"),                          myfile$letter, value=true))

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