grep using a character vector with multiple patterns

Question

I am trying to use grep to test whether a vector of strings are present in an another vector or not, and to output the values that are present (the matching pat

Answer 1

To add to Brian Diggs answer.

another way using grepl will return a data frame containing all your values.

toMatch <- myfile$Letter

matches <- myfile[grepl(paste(toMatch, collapse="|"), myfile$Letter), ]

matches

Letter Firstname
1     A1      Alex 
2     A6      Alex 
4     A1       Bob 
5     A9     Chris 
6     A6     Chris

Maybe a bit cleaner... maybe?

Answer 2

Good answers, however don't forget about filter() from dplyr:

patterns <- c("A1", "A9", "A6")
>your_df
  FirstName Letter
1      Alex     A1
2      Alex     A6
3      Alex     A7
4       Bob     A1
5     Chris     A9
6     Chris     A6

result <- filter(your_df, grepl(paste(patterns, collapse="|"), Letter))

>result
  FirstName Letter
1      Alex     A1
2      Alex     A6
3       Bob     A1
4     Chris     A9
5     Chris     A6

Answer 3

This should work:

grep(pattern = 'A1|A9|A6', x = myfile$Letter)

Or even more simply:

library(data.table)
myfile$Letter %like% 'A1|A9|A6'

Answer 4

Using the sapply

 patterns <- c("A1", "A9", "A6")
         df <- data.frame(name=c("A","Ale","Al","lex","x"),Letters=c("A1","A2","A9","A1","A9"))



   name Letters
1    A      A1
2  Ale      A2
3   Al      A9
4  lex      A1
5    x      A9


 df[unlist(sapply(patterns, grep, df$Letters, USE.NAMES = F)), ]
  name Letters
1    A      A1
4  lex      A1
3   Al      A9
5    x      A9

Answer 5

Take away the spaces. So do:

matches <- unique(grep("A1|A9|A6", myfile$Letter, value=TRUE, fixed=TRUE))

Answer 6

Not sure whether this answer has already appeared...

For the particular pattern in the question, you can just do it with a single grep() call,

grep("A[169]", myfile$Letter)