R help - Feb 2010 - Help with apply()

I have a 2 column data.frame:

 > d[1:5,]
   a b
1    80015     C
2    80016     B
3    80023     C
4    80062     B
5    80069     B

I want to apply a function across each row:

 > for(i in 1:nrow(d)) {
+    myFun(con, d[i,]$a, d[i,]$b)
+ }

How do I do this using apply()? I'm unsure how to tell apply() to pass 
data from columns a and b for a given row as arguments to the function 
myFun().

Thanks in advance for any pointers,
Nathan

-- 
--------------------------------------------------------
Dr. Nathan S. Watson-Haigh
OCE Post Doctoral Fellow
CSIRO Livestock Industries
University Drive
Townsville, QLD 4810
Australia

Tel: +61 (0)7 4753 8548
Fax: +61 (0)7 4753 8600
Web: http://www.csiro.au/people/Nathan.Watson-Haigh.html

On Feb 7, 2010, at 8:26 PM, Nathan S. Watson-Haigh wrote:
> I have a 2 column data.frame:
>
> > d[1:5,]
>  a b
> 1    80015     C
> 2    80016     B
> 3    80023     C
> 4    80062     B
> 5    80069     B
>
> I want to apply a function across each row:
>
> > for(i in 1:nrow(d)) {
> +    myFun(con, d[i,]$a, d[i,]$b)
> + }
>
> How do I do this using apply()? I'm unsure how to tell apply() to  
> pass data from columns a and b for a given row as arguments to the  
> function myFun().
apply(d, 1, function(x) myFun(x[1], x[2]) )

The reason you cannot use the "$" operator is that the row is passed  
to the function as a vector, rather than as a list.

-- 
David
>
> Thanks in advance for any pointers,
> Nathan
>
> -- 
> --------------------------------------------------------
> Dr. Nathan S. Watson-Haigh
> OCE Post Doctoral Fellow
> CSIRO Livestock Industries
> University Drive
> Townsville, QLD 4810
> Australia
>
> Tel: +61 (0)7 4753 8548
> Fax: +61 (0)7 4753 8600
> Web: http://www.csiro.au/people/Nathan.Watson-Haigh.html
>
> ______________________________________________
> R-help at 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.

On 02/08/2010 12:26 PM, Nathan S. Watson-Haigh wrote:
> I have a 2 column data.frame:
>
>  > d[1:5,]
> a b
> 1 80015 C
> 2 80016 B
> 3 80023 C
> 4 80062 B
> 5 80069 B
>
> I want to apply a function across each row:
>
>  > for(i in 1:nrow(d)) {
> + myFun(con, d[i,]$a, d[i,]$b)
> + }
>
> How do I do this using apply()? I'm unsure how to tell apply() to pass
> data from columns a and b for a given row as arguments to the function
> myFun().
>
Hi Nathan,
apply doesn't work with data frames unless they can be coerced to 
matrices or arrays (and sometimes not even then). What's wrong with 
using the code you have above?

Jim