Question

I have 2 extracted data sets from a dataset called babies2009( 3 vectors count, name, gender )

One is girls2009 containing all the girls and the other boys2009.
I want to find out what similar names exist between boys and girls.

I tried this

common.names = (boys2009$name %in% girls2009$name)

When I try

babies2009[common.names, ] [1:10, ]

all I get is the girl names not the common names.

I have confirmed that both data sets indeed contain boys and girls respectively by doing taking a 10 sample…

boys2009 [1:10,]
girsl2009 [1:10,]

How else can I compare the 2 datasets and determine what values they both share.
Thanks,

Answer 1

common.names = (boys2009$name %in% girls2009$name) gives you a logical vector of length length(boys2009$name). So when you try selecting from a much longer data.frame babies2009[common.names, ] [1:10, ], you wind up with nonsense.

Solution: use that logical vector on the proper data.frame!

boys2009 <- data.frame( names=c("Billy","Bob"),data=runif(2), gender="M" , stringsAsFactors=FALSE)
girls2009 <- data.frame( names=c("Billy","Mae","Sue"),data=runif(3), gender="F" , stringsAsFactors=FALSE)
babies2009 <- rbind(boys2009,girls2009)

common.names <- (boys2009$name %in% girls2009$name)

> boys2009[common.names, ]$names
[1] "Billy"