[R] use of apply in a data frame on a row by row basis

[Gabor Grothendieck]

On 7/6/06, Julien Laugel <roolio4news at gmail.com> wrote:
> Hello all,
>
> I'm trying to use the apply function on a data frame,
> by applying a function that takes a one row data.frame as argument .
>
> Here's the example :
> myfun = function(x) paste(x$f1 , x$f2)
> df = data.frame(f1 = c(1,4,10),f2 = "hello")
>
> apply(df,1,myfun) ==> Does not work (I get "character(0)" )

Try one of these:

sapply(split(df, rownames(df)), myfun)
sapply(1:nrow(df), function(i) paste(df$f1[i], df$f2[i]))
sapply(1:nrow(df), function(i) paste(df[i,1], df[i,2]))

>
> Though : myfun(df[1,]) works,
> and myfun(df) works as well.
>
> So if myfun(df) works, that's fine!
> BUT, if the output of the function a bit more complex, it does not work :
> In this case I'm using a timeSeries object (from Rmetrics)
>
> library(fMultivar)
> timerange = timeSequence(from = "2001-04-11", length.out = 3,by = "weeks",
> format = "%Y-%m-%d", FinCenter = "GMT")
> myfun2 = function(x) timeSeries(rnorm(3),timerange)
>
> In this case, myfun2(df) returns only the result of the 1st row!
> BUT
> apply(df,1,myfun2) in this case, does work
>
> But I haven't used the "$" notation to access one field
> Now if I try (and that is the cas that bugs me currently) :
>
> myfun3 = function(x) timeSeries(rep(x$f1,3),timerange)
>
> myfun3(df)
> Error in "rownames<-"(`*tmp*`, value = c("2001-04-11 02:00:00", "2001-04-18
> 02:00:00", :
> length of 'dimnames' [1] is not equal to range of the array
> (sorry for the translation : I'm using a french version of R)
> Though
> > myfun3(df[1,])
> TS.1
> 2001-04-11 02:00:00 1
> 2001-04-18 02:00:00 1
> 2001-04-25 02:00:00 1
> works well
> BUT :
> apply(df,1,myfun3)
> yields :
>
> Error in array(x, c(length(x), 1), if (!is.null(names(x))) list(names(x), :
> trying to change an attribute in NULL
>
> So as a result I'm verry annoyed, and I don't see the logic behind.
> How can I do to make a apply-like function on the latter function? (myfun3)
>
> Many thanks in advance
>
> Regards,
>
> Roolio
>
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