R help - Dec 2010 - How to pass selection criteria in a function

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!


Chris McCarthy, PhD
Department of Mathematics BMCC
Office: N522   Extension: 5235
cmccarthy@bmcc.cuny.edu
	[[alternative HTML version deleted]]

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

Try this:

newTable <- function(data, criteria) {
    do.call(subset, list(data, substitute(criteria)))
}

On Wed, Dec 1, 2010 at 3:56 PM, <CMcCarthy@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!
>
>
> Chris McCarthy, PhD
> Department of Mathematics BMCC
> Office: N522   Extension: 5235
> cmccarthy@bmcc.cuny.edu
>        [[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

Thank you all for your very fast replies.

I tried Henrique's method (see one of the above posts) , and it works
perfectly!
Thanks again!
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