[R] apply in apply

[baptiste Auguié]

Thank you for the suggestions (off-list as well). I think the best  
option may eventually be an explicit for loop to make things clearer.  
To clarify a bit, I've used the plot function in the example where in  
fact it is a numerical integration (which is why I need to pass an  
additional variable in the second apply call),

> intg <- function (y, x)
> {
>     n <- length(x)
>     index <- order(x)
>     dx <- diff(sort(x))
>     z <- y[index]
>     ys <- (z[1:(n - 1)] + z[2:n])/2
>     sum(ys * dx)
> }
> <environment: namespace:PROcess>


Thanks again for the suggestions,

baptiste

On 30 May 2008, at 10:02, Richard.Cotton at hsl.gov.uk wrote:

>> I need to apply a function on each column of each matrix contained in
>> a list. Consider the following code,
>>
>>> x <- 1:3
>>> my.data <- list(matrix(c(1,2,3,4,5,6),ncol=2),
>>>       matrix(c(4,5,6,7,8,9),ncol=2))
>>>
>>> par(mfrow=c(2,2))
>>> results <- sapply(1:length(my.data),
>>>          function(ii) apply(my.data[[ii]], 2, function(y) plot 
>>> (x,y) ))
> #
>>> plot is for demonstration purposes
>>
>>
>> It works, but I think this is quite dirty code. Is there a simpler
>> way of achieving this?
>
> The last line can be simplified
> results <- sapply(my.data, function(x) apply(x,2,sum))
>
> (It is perhaps a little clearer what is going on when you use sum  
> rather
> than plot as the example function.)
>
> Regards,
> Richie.
>
> Mathematical Sciences Unit
> HSL
>
>
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