Existing function for seeing if a row exists in a data frame?

Question

Is there an existing function for determining whether a row exists within a data frame? I suppose could do an apply/identical, but it seems like I'm missing something.

For example:

given such a data frame:

  a   b
1 1 cat
2 2 dog

Is there an existing function which will allow me to test whether the row (1, cat) exists in the data frame?

Thanks, Zach

Answer 1

Try match_df from plyr (using Marek's sample data):

library(plyr)
X <- data.frame(a=1:2, b=c("cat","dog"))
row_to_find <- data.frame(a=1, b="cat")

match_df(X, row_to_find)

Answer 2

For data from @Marek answer.

nrow(merge(row_to_find,X))>0 # TRUE if exists

Answer 3

Taking your example:

X <- data.frame(a=1:2, b=c("cat","dog"))
row_to_find <- data.frame(a=1, b="cat") # it has to be data.frame (not a vector) to hold different types

Then

duplicated(rbind(X, row_to_find))[nrow(X)+1]

gives you answer.

Answer 4

I suggest Ben Bolker's solution since nrow(merge(row_to_find,X))>0 solution doesn't work for me (always give TRUE) :

tail(duplicated(rbind(X,row_to_find)),1)>0