[R] mapply on multiple data frames

[Webb,Elizabeth E]

Hi all-

I am wondering about using the mapply function to multiple data frames.  Specifically, I would like to do a t-test on a subset of multiple data frames.  All data frames have the same structure.
Here is my code so far:

f<-function(x,y) {
test<-t.test(x$col1[x$col3=="num",],v$col2[x$col3=="num",],paired=T,alternative="greater")
out<-test$p.value
return(out) 
}

all_nums<-list(num1,num2,num3,num4)
all_dfs<-list(df1,df2,df3,df4)

mapply(f,all_dfs,all_nums)


This tells me that $ operator is invalid for atomic vectors.  I have tried shifting to notation using [  ,] to denote columns, but that gives me this error: incorrect number of dimensions.  

Thank you in advance,
Elizabeth