使.combine函数可缩放 [英] make .combine function scaleable
问题描述
我正在尝试使用foreach,并且遇到了使.combine函数可扩展的问题。例如,下面是一个简单的组合函数:
pre $ MyComb < - function(part1,part2){
xs< (part1 $ x,part2 $ x)
ys <-c(part1 $ y,part2 $ y)
return(list(xs,ys))
}
当我使用这个函数将一个foreach语句与一个不是2的迭代器结合起来时,它会错误地返回它。例如这个工程:
pre $ x $ foreach(i = 1:2,.combine = MyComb)%dopar%list( x= i * 2,y= i * 3)
p>
x = foreach(i = 1:3,.combine = MyComb)%dopar%list(x= i * 2, y= i * 3)
是否有一种方法可以扩展组合函数以使其可扩展到n次迭代? 看起来像一块(可以作为一个部分传回去),或者采取许多论据,并把它们同时放在一起(具有相同的限制)。因此,至少你的 MyComb
必须返回一个包含组件 x
和 y $ c的列表$ c>(这就是你的每一块
%dopar%
所做的。
有几种方法可以做这:
MyComb1< - function(part1,part2){
list(x = c(part1 $ x ,part2 $ x),y = c(part1 $ y,part2 $ y))
}
x = foreach(i = 1:3,.combine = MyComb1)%dopar%list (x= i * 2,y= i * 3)
MyComb2< - function(...){
dots = list(。 ...)
ret < - lapply(names(dots [[1]]),function(e){
unlist(sapply(dots,'[[',e))
})
name(ret)< - names(dots [[1]])
ret
}
s = foreach(i = 1:3 ,. combine = MyComb2)%dopar%list(x= i * 2,y= i * 3)
x = foreach(i = 1:3,.combine = MyComb2,.multicombine = TRUE)%dopar %list(x= i * 2,y= i * 3)
可以采取多个piec es一次结合起来。这是更一般(但更复杂)。
I am trying to use foreach and am having problems making the .combine function scalable. For example, here is a simple combine function
MyComb <- function(part1,part2){
xs <- c(part1$x,part2$x)
ys <- c(part1$y,part2$y)
return(list(xs,ys))
}
When I use this function to combine a foreach statement with an iterator other than 2 it returns it incorrectly. For example this works:
x = foreach(i=1:2,.combine=MyComb) %dopar% list("x"=i*2,"y"=i*3)
But not this:
x = foreach(i=1:3,.combine=MyComb) %dopar% list("x"=i*2,"y"=i*3)
Is there a way to generalize the combine function to make it scalable to n iterations?
Your .combine
function must take either two pieces and return something that "looks" like a piece (could be passed back in as a part) or take many arguments and put all of them together at once (with the same restrictions). Thus at least your MyComb
must return a list with components x
and y
(which is what each piece of your %dopar%
do.
A couple of ways to do this:
MyComb1 <- function(part1, part2) {
list(x=c(part1$x, part2$x), y=c(part1$y, part2$y))
}
x = foreach(i=1:3,.combine=MyComb1) %dopar% list("x"=i*2,"y"=i*3)
This version takes only two pieces at a time.
MyComb2 <- function(...) {
dots = list(...)
ret <- lapply(names(dots[[1]]), function(e) {
unlist(sapply(dots, '[[', e))
})
names(ret) <- names(dots[[1]])
ret
}
s = foreach(i=1:3,.combine=MyComb2) %dopar% list("x"=i*2,"y"=i*3)
x = foreach(i=1:3,.combine=MyComb2, .multicombine=TRUE) %dopar% list("x"=i*2,"y"=i*3)
This one can take multiple pieces at a time and combine them. It is more general (but more complex).
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