How to pass selection criteria in a function
On Wed, 1 Dec 2010, CMcCarthy at bmcc.cuny.edu wrote:
Hi,
Suppose I have the following data
name???? score
Abel??????? 88
Baker????? 54
Charlie??? 77
stored a? table called myData.
I want to write a function that will create a table which is a subset of myData containing those have a score > 75.
I know I can do this with the following command:
subset(myData, score > 75)
But I would like to do this via a function, something like:
newTable <- function( data,? criteria){
??????????????????? subset( data, criteria) }
and then calling:???? newTable(myData, score > 75)
But this doesn't work. I am sure there is a simple way to do this,
but I am stuck! Please help. Thanks!
Simple? Maybe not so much! You are trying to pass objects without evaluating them. subset is rather special in the way it works. Here is one way:
foo <- function(x,...){
+ mc <- match.call()
+ mc[[1]] <- as.name("subset")
+ eval(mc)
+ }
foo(iris, Petal.Width>2.4 )
Sepal.Length Sepal.Width Petal.Length Petal.Width Species 101 6.3 3.3 6.0 2.5 virginica 110 7.2 3.6 6.1 2.5 virginica 145 6.7 3.3 5.7 2.5 virginica Reading the code at the top of lm shows how this kind of strategy can be used. You might look at ?bquote for another way to skin this cat. HTH, Chuck
Chris?McCarthy, PhD Department?of?Mathematics?BMCC Office:?N522???Extension:?5235 cmccarthy at bmcc.cuny.edu [[alternative HTML version deleted]]
Charles C. Berry Dept of Family/Preventive Medicine cberry at tajo.ucsd.edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901