[R] Basic question on applying a function to each row of a da taframe

[Sundar Dorai-Raj]

Yes, but very slow for this example when the data.frame gets large....

R> DF <- data.frame(x = rnorm(40000), y = rnorm(40000))
R> foo <- function(z, x, y) z[x] + z[y]
R> bar <- function(x, y) x + y
R> system.time(x <- apply(DF, 1, foo, x = "x", y = "y"))
[1] 6.94 0.04 7.37   NA   NA
R> system.time(y <- with(DF, bar(x, y))) # from A. Liaw
[1] 0.01 0.00 0.01   NA   NA
R> all(x == y)
[1] TRUE
R> system.time(z <- mapply("bar", DF[,1], DF[,2]))

Timing stopped at: 145.49 0.26 156.74 NA NA
R> # not sure why mapply doesn't work here...

Best,
Sundar

Ramzi Feghali wrote:
> Another another neat way is:
>  
> 
>>DF <- data.frame(x=1:4, y=rep(1,4))
>>foo <- function(z,x,y)z[x]+z[y]
>>apply(DF,1,foo,x="x",y="y")
> 
> 1 2 3 4 
> 2 3 4 5 
>  
> or
>  
> 
>>DF <- data.frame(x=1:4, y=rep(1,4))
>>foo <- function(z)z<-x+y
>>foo(DF)
> 
> [1] 2 3 4 5
> 
> 
> "Liaw, Andy" <andy_liaw at merck.com> wrote:
> Another neat way is:
> 
> with(DF, foo(x, w))
> 
> HTH,
> Andy
> 
> 
>>-----Original Message-----
>>From: peter leonard [mailto:pfleonard at hotmail.com]
>>Sent: Sunday, June 08, 2003 4:35 PM
>>To: r-help at stat.math.ethz.ch
>>Subject: [R] Basic question on applying a function to each row of a
>>dataframe
>>
>>
>>Hi,
>>
>>I have a function foo(x,y) and a dataframe, DF, comprised of 
>>two vectors, x 
>>& w, as follows :
>>
>>x w
>>1 1 1
>>2 2 1
>>3 3 1
>>4 4 1
>>
>>etc
>>
>>
>>I would like to apply the function foo to each 'pair' within DF e.g 
>>foo(1,1), foo(2,1), foo(3,1) etc
>>
>>I have tried
>>
>>
>>>apply(DF,foo)
>>>apply(DF[,],foo)
>>>apply(DF[DF$x,DF$w],foo)
>>
>>
>>However, none of the above worked. Can anyone help ?
>>
>>Thanks in advance,
>>Peter
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>>
> 
> 
> ------------------------------------------------------------------------------
> Notice: This e-mail message, together with any attachments, cont... {{dropped}}
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 
> 
> ---------------------------------
> 
> 
> 	[[alternate HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>