R selecting all rows from a data frame that don't appear in another

Question

I'm trying to solve a tricky R problem that I haven't been able to solve via Googling keywords. Specifically, I'm trying to take a subset one data frame whose values don't appear in another. Here is an example:

> test
      number    fruit     ID1  ID2 
item1 "number1" "apples"  "22" "33"
item2 "number2" "oranges" "13" "33"
item3 "number3" "peaches" "44" "25"
item4 "number4" "apples"  "12" "13"
> test2
      number    fruit     ID1   ID2 
item1 "number1" "papayas" "22"  "33"
item2 "number2" "oranges" "13"  "33"
item3 "number3" "peaches" "441" "25"
item4 "number4" "apples"  "123" "13"
item5 "number3" "peaches" "44"  "25"
item6 "number4" "apples"  "12"  "13"
item7 "number1" "apples"  "22"  "33"

I have two data frames, test and test2, and the goal is to select all entire rows in test2 that don't appear in test, even though some of the values may be the same.

The output I want would look like:

item1 "number1" "papayas" "22"  "33"
item2 "number3" "peaches" "441" "25"
item3 "number4" "apples"  "123" "13"

There may be an arbitrary amount of rows or columns, but in my specific case, one data frame is a direct subset of the other.

I've used the R subset(), merge() and which() functions extensively, but couldn't figure out how to use these in combination, if it's possible at all, to get what I want.

edit: Here is the R code I used to generate these two tables.

test <- data.frame(c("number1", "apples", 22, 33), c("number2", "oranges", 13, 33),
    c("number3", "peaches", 44, 25), c("number4", "apples", 12, 13))

test <- t(test)
rownames(test) = c("item1", "item2", "item3", "item4")
colnames(test) = c("number", "fruit", "ID1", "ID2")

test2 <- data.frame(data.frame(c("number1", "papayas", 22, 33), c("number2", "oranges", 13, 33),
    c("number3", "peaches", 441, 25), c("number4", "apples", 123, 13),c("number3", "peaches", 44, 25), c("number4", "apples", 12, 13)  ))

test2 <- t(test2)
rownames(test2) = c("item1", "item2", "item3", "item4", "item5", "item6")
colnames(test2) = c("number", "fruit", "ID1", "ID2")

Thanks in advance!

Answer 1

Here's another way:

x <- rbind(test2, test)
x[! duplicated(x, fromLast=TRUE) & seq(nrow(x)) <= nrow(test2), ]
#        number   fruit ID1 ID2
# item1 number1 papayas  22  33
# item3 number3 peaches 441  25
# item4 number4  apples 123  13

Edit: modified to preserve row names.