R help - Jul 2005 - Using a string as a filter

On 7/10/05, Yzhar Toren <torenizh at post.tau.ac.il>
wrote:
> Hi ,
> 
> I want to be able to filter out results using a string. I'm running an
> automated script that reads a list of filters I get from an external
> source and applys them to my data frame consecutively.
> 
> For example I want to get : data[protocol==1], data[protocol==2] ...
> 
> If I define
> filter1 <- "protocol==1" (as a string)
> filter2 <- "protocol==2"
> ...
protocol <- 1:5
data <- 11:15
filter <- "protocol==1"
data[eval(parse(text=filter))] # 11

Hi ,

I want to be able to filter out results using a string. I'm running an 
automated script that reads a list of filters I get from an external 
source and applys them to my data frame consecutively.

For example I want to get : data[protocol==1], data[protocol==2] ...

If I define
filter1 <- "protocol==1" (as a string)
filter2 <- "protocol==2"
...
How can I use these variables to choose subsets ?

I managed to find a very awkward method by using a function that calls a 
formula (and using as.formula() for the string I want to get), but I 
would love to find a more efficient way

Thank you !
Yzhar Toren, Tel-Aviv university.