R help - Jan 2012 - 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,to=100, length.out=30)
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!

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Hi,

On Thu, Jan 12, 2012 at 3:10 PM, dadrivr <dadrivr at gmail.com>
wrote:
> 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,to=100, length.out=30)
> keepid <- c(6,10,12,13,19,25,26,27,28,29)
You won't get two columns unless you create a data frame rather than a
regular list.

mydata <- data.frame(id = 1:30, value = seq(from=1,to=100, length.out=30))
> 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!
Here are two ways; more exist.

mydata[mydata$id %in% keepid, ]
subset(mydata, mydata$id %in% keepid)

Thanks for including a small reproducible example.

Sarah

-- 
Sarah Goslee
http://www.functionaldiversity.org