How do I use grep on a data frame?

Question

I have the following data frame:

> my.data
  A.Seats    B.Seats
1   14,15   14,15,16
2       7        7,8
3   12,13      16,17
4    <NA>      10,11

I would like to check if the string within any row in column "A.Seats" is found within the same row of column "B.Seats". So the output would look something like this:

  A.Seats    B.Seats    Check
1   14,15   14,15,16     TRUE
2       7        7,8     TRUE
3   12,13      16,17    FALSE
4    <NA>      10,11    FALSE

But I don't know how to create this table. As a start, I tried using grep:

grep(my.data$A.Seats,my.data$B.Seats)

But I receive the following output

[1] 1
Warning message:
In grep(my.data$A.Seats, my.data$B.Seats) :
argument 'pattern' has length > 1 and only the first element will be used

...and I can't get past this error. Any ideas as to how I can get the intended result?

Many Thanks

Answer 1

The "stringi" library has some vectorized functions that might be useful for something like this. I would suggest the stri_detect() function. Here's an example with some reproducible sample data. Note the difference in the values in the first and last row, and the difference in the results according to whether a regex or fixed approach was taken:

my.data <- data.frame(
    A.Seats = c("14,15", "7", "12,13", NA, "14,19"),
    B.Seats = c("14,15,16", "7,8", "16,17", "10,11", "14,15,16"))
my.data
#   A.Seats  B.Seats
# 1   14,15 14,15,16
# 2       7      7,8
# 3   12,13    16,17
# 4    <NA>    10,11
# 5   14,19 14,15,16

library(stringi)
stri_detect(my.data$B.Seats, fixed = my.data$A.Seats)
# [1]  TRUE  TRUE FALSE    NA FALSE
stri_detect(my.data$B.Seats, regex = gsub(",", "|", my.data$A.Seats))
# [1]  TRUE  TRUE FALSE    NA  TRUE

The first option above treats the values in my.data$A.Seats as a fixed string pattern. The second option treats it as a regular expression to match any of the values.

Note that this maintains NA as NA, but that can easily be changed to FALSE if you need to.

---

If you don't want to think too much about mapply, you can consider Vectorize to make a vectorized version of grepl. Something like the following should do it:

vGrepl <- Vectorize(grepl)
vGrepl(my.data$A.Seats, my.data$B.Seats)                 # pattern is fixed
# [1]  1  1  0 NA  0
vGrepl(gsub(",", "|", my.data$A.Seats), my.data$B.Seats) # pattern is regex
# 14|15     7 12|13  <NA> 14|19 
#     1     1     0    NA     1 
as.logical(vGrepl(my.data$A.Seats, my.data$B.Seats))     # coerce to logical
# [1]  TRUE  TRUE FALSE    NA FALSE

Because this calls grepl on each element in the vector, I don't think this will scale well though.