嵌套的R foreach循环中的外循环变量 [英] Outer loop variable in nested R foreach loop

问题描述

我试图在嵌套循环中使用foreach包，但是我的内部循环没有识别出外部的计数器，我错过了什么？

<$ p $ （100.05,0.5）
foreach（j = 2：length（v2））％：％{
foreach（i = 1：length（v3），.combine = rbind）％dopar％{
write.table（paste（v3 [i]，paste（get.reactions.by.compound（v3 [i]），collapse = ），sep =），file1，quote = FALSE，row.names = FALSE，col.names = FALSE，append = TRUE）
write.table（paste（v3 [i] （get.pathways.by.compounds（v3 [i]），collapse =），sep =），file2，quote = FALSE，row.names = FALSE，col.names = FALSE，append = TRUE ）
v3< - search.compounds.by.mass（v2 [j]，0.5）
}
}
％：％操作符。它被设计为合并两个 foreach 对象，产生一个单独的 foreach 对象，可用于重复评估任何表达式你提供给它。所以，如果你想使用％：％，你需要第一合并两个 foreach（）语句，然后然后使用结果对象驱动一个调用到％do％（或者在你的情况下，％dopar％）。以下（1）为例。另外，如果你想嵌套两个 foreach（）对象，使用％做％两次，就像下面的（2）一样。

无论哪种方式都行得通，更喜欢使用％：％的那个。你的代码虽然像下面的（3）那样，结合了两个策略的元素来产生一个混合，它不能做任何事情。

<$ p （1）或者合并两个或者两个以上的元素，并且将两个元素合并'foreach'对象使用'％：％'...
foreach（j = X，.combine = c）％：％foreach（i = Y，.combine = c）％do％{
粘贴（j，i，sep =）
}
＃[1]A1A2A3B1B2B3


##（2）...或者使用一对'％do％'操作符嵌套两个'foreach'对象...
foreach（j = X，.combine = c）％do％ {
foreach（i = Y，.combine = c）％do％{
paste（j，i，sep =）
}
}
＃ [1]A1A2A3B1B2B3


##（3）...但不要使用混合方法。
foreach（j = X，.combine = c）％：％{
foreach（i = Y，.combine = c）％do％{
paste（j，i，sep = ）

$ b $ foreach（j = X，.combine = c）中的错误％：％{：
＃％：％右操作数

I'm trying to use the foreach package in a nested loop, but my inner loop don't recognizes the outer's counter, what m I missing?

v3 <- search.compounds.by.mass(100.05,0.5)
foreach(j=2:length(v2)) %:% {
    foreach(i=1:length(v3), .combine=rbind) %dopar% {
        write.table(paste(v3[i], paste(get.reactions.by.compound(v3[i]), collapse=" "), sep=" "), "file1",quote=FALSE, row.names=FALSE, col.names=FALSE, append=TRUE)
        write.table(paste(v3[i], paste(get.pathways.by.compounds(v3[i]), collapse=" "), sep=" "), "file2",quote=FALSE, row.names=FALSE, col.names=FALSE, append=TRUE)
        v3 <- search.compounds.by.mass(v2[j],0.5)
    }
}

解决方案

The problem is that you are incorrectly applying the %:% operator. It is designed to merge two foreach objects, resulting in a single foreach object that can be used to repeatedly evaluate whatever expression you supply to it. So, if you want to use %:%, you need to first merge the two foreach() statements, and then use the resulting object to drive a single call to %do% (or in your case, %dopar%). See (1) below for an example.

Alternatively, if you want to nest the two foreach() objects, use %do% twice, as in (2) below.

Either way works, although for parallel jobs I might prefer the one using %:%. Your code, though, like (3) below, combines elements of the two strategies to produce a hybrid that can't do anything.

X <- c("A", "B")
Y <- 1:3

## (1) EITHER merge two 'foreach' objects using '%:%' ...
foreach (j = X, .combine = c) %:% foreach(i = Y, .combine = c) %do% {
    paste(j, i, sep = "")
}
# [1] "A1" "A2" "A3" "B1" "B2" "B3"


## (2) ... OR Nest two 'foreach' objects using a pair of '%do%' operators ...
foreach(j = X, .combine = c) %do% {
    foreach(i = Y, .combine = c) %do% {
        paste(j, i, sep = "")
    }
}
# [1] "A1" "A2" "A3" "B1" "B2" "B3"


## (3) ... BUT DON'T use a hybrid of the approaches.
foreach(j = X, .combine = c) %:% {
    foreach(i = Y, .combine = c) %do% {
        paste(j, i, sep = "")
    }
}
# Error in foreach(j = X, .combine = c) %:% { : 
#   "%:%" was passed an illegal right operand

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