[R] Keep rows where a variable matches one item of a vector

How do I subset data to only keep those rows of a dataframe where a
variable's value matches one item of a vector. For example, how do I keep
all of the rows (and all variables) where mydata$id equals one of the values
in keepid? See below?

mydata <- NULL
mydata$id <- 1:30
mydata$value <- seq(from=1,to0, length.out0)
keepid <- c(6,10,12,13,19,25,26,27,28,29)

In other words, I want the output file to have two columns, 1) id and 2)
value, with only those rows where id equals one of the values in the keepid
vector. Thanks for your help!