Check whether a row with values belongs to a data frame in R [duplicate]

Question

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

Suppose I have the following data frame in R.

df = data.frame('a'=c(1:3), 'b'=c(4:6))

This data frame contains three rows: (1,4), (2,5) and (3,6). Suppose I did not know which rows df contains and wanted to check whether a row (1,4) belongs to it, how can I check that?

My actual case involves comparison of 27 parameter values. Is there a solution in which I can do this without typing each and every parameter name? Thanks!

The reason I want to do this is that I have an R dataset called masterdata which contains simulation data. I want to update this data set with new data that is obtained as I make additional simulation runs with different parameter combinations. It is possible, however, that I may forget that I have run the simulation for a certain parameter combination and may run it again, in which case, the masterdata will be expanded with duplicate values. I can later go and remove these duplicate values, but I would not want the whole process of updating the data set to go through if the values are duplicate. For this I need to check if the data from a simulation run is already present in the masterdata. I can do this if I know how to check whether a given row belongs to the masterdata.

Thanks.

Answer 1

There may be more efficient ways, but I think

tail(duplicated(rbind(masterdata,newvals)),1)

will do it: in other words, attach the new row to the end of the data frame and see whether it is duplicated or not.