[R] Testing for membership in an array of strings

[Marc Schwartz]

On Jul 2, 2009, at 9:13 AM, Neil Tiffin wrote:

> As an R beginner, I feel brain dead today as I can not find the  
> answer to a relatively simple question.
>
> Given a array of string values, for example lets say "mary", "bob",  
> "danny", "sue", and "jane".
>
> I am trying to determine how to perform a logical test to determine  
> if a variable is an exact match for one of the string values in the  
> array when the number of strings in the array is variable and  
> without using a for loop and without comparing each value.   
> Considering the power of R, I thought this would be easy, but its  
> not obvious to me.
>
> Now I may not yet be one with the R fu so a bit more context.
>
> I have a data frame that contains a column with text values. What I  
> am trying to do is use the subset function on the data frame to  
> select only data for "sue" or "jane" (for example.)  But maybe I  
> have not taken the correct approach?
>
> So obviously I could do something like the following.
>
> subset( data_frame, name = "sue" | name == "jane", select = c(name,  
> age, birthdate))
>
> However, my subset needs to be much more than 2 and being lazy I do  
> not want to type "| name == "some text" for each one.
>
> Is there an other way?
>
> Neil

Try this:

   subset(data_frame, name %in% c("sue", "jane"), select = c(name,  
age, birthdate))

or if your vector of names is:

   Names <-  c("mary", "bob", "danny", "sue", "jane")

   subset(data_frame, name %in% Names, select = c(name, age, birthdate))


See ?"%in%" for more information.

HTH,

Marc Schwartz