[R] Subsetting a data frame
natalie.vanzuydam
nvanzuydam at gmail.com
Mon Dec 5 12:32:10 CET 2011
Hi R users,
I really need help with subsetting data frames:
I have a large database of medical records and I want to be able to match
patterns from a list of search terms .
I've used this simplified data frame in a previous example:
db <- structure(list(ind = c("ind1", "ind2", "ind3", "ind4"), test1 = c(1,
2, 1.3, 3), test2 = c(56L, 27L, 58L, 2L), test3 = c(1.1, 28,
9, 1.2)), .Names = c("ind", "test1", "test2", "test3"), class =
"data.frame", row.names = c(NA,
-4L))
terms_include <- c("1","2","3")
terms_exclude <- c("1.1","1.2","1.3")
So in this example I want to include all the terms from terms include as
long as they don't occur with terms exclude in the same row of the data
frame.
Previously I was given this function which works very well if you want to
match exactly:
f <- function(x) !any(x %in% terms_exclude) && any(x %in% terms_include)
db[apply(db[, -1], 1, f), ]
ind test1 test2 test3
2 ind2 2 27 28.0
4 ind4 3 2 1.2
I would like to know if there is a way to write a similar function that
looks for matches that start with the query string: as in
grepl("^pattern",x)
I started writing a function but am not sure how to get it to return the
dataframe or matrix:
for (i in 1:length(terms_include)){
db_new <- apply(db,2, grepl,pattern=i)
}
Applying this function gives me:
db_new <- structure(c(FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, TRUE, TRUE,
FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE), .Dim = c(4L,
4L), .Dimnames = list(NULL, c("ind", "test1", "test2", "test3"
)))
So the above is searching the pattern anywhere in the dataframe instead of
just at the beginning of the string.
How would I incorporate look for terms to include but don't return the row
of the data frame if it also includes one of the terms to exclude while
using partial matching?
I hope that this makes sense.
Many thanks,
Natalie
-----
Natalie Van Zuydam
PhD Student
University of Dundee
nvanzuydam at dundee.ac.uk
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