[R] How to pass selection criteria in a function
Charles C. Berry
cberry at tajo.ucsd.edu
Wed Dec 1 19:12:51 CET 2010
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
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