在R中就地修改矩阵 [英] In place modification of matrices in R

问题描述

我有什么方法可以避免对R中的矩阵进行原位修改吗?

I there any way to avoid copy-on-modify for in-place modifications of matrices in R?

我正尝试将较小的矩阵复制到较大的矩阵的切片，如下所示.

I am trying to copy a smaller matrix to a slice of larger matrix as follows.

library(data.table)
y <- matrix(c(11,21,31,12,22,32),nrow=3,ncol=2)
address(y)
[1] "08429190"

y[2:3,] <- matrix(c(1,1,8,12),nrow=2)
address(y)
[1] "0E033D28"

推荐答案

使用在Windows 8.1上的RStudio 0.99.441中运行的R 3.2.0，并使用pryr::address，我得到的操作与OP相同.问题是RStudio的环境"窗格对y进行了引用.通常， Hadley Wickham 对此都有很好的说明.

I get the same behaviour as the OP using R 3.2.0 running within RStudio 0.99.441 on Windows 8.1 and using pryr::address. The issue is RStudio has a reference to y for its Environment pane. As often the case, Hadley Wickham has some excellent documentation of this.

除了不使用RStudio之外，对于全球环境中的矩阵，我认为没有其他方法可以解决此问题.我已经尝试了其他几件事.函数中的矩阵很好:

I don't think there's any way around this for matrices in the global environment other than not using RStudio. I've tried a couple of other things. Matrices within a function are fine:

library("pryr")
fn <- function() {
  y <- matrix(c(11,21,31,12,22,32),nrow=3,ncol=2)
  print(address(y))
  y[2:3,] <- matrix(c(1,1,8,12),nrow=2)
  print(address(y))
}

呼叫fn()应该显示地址不变.

Calling fn() should show that the address is unchanged.

但是，将y创建为全局环境中的列表或环境的成员并不会阻止写入时的复制(例如x <- new.env(); x$y <- matrix(...)).

However, creating y as a member of a list or environment which are in the global environment doesn't prevent the copy on write (e.g. x <- new.env(); x$y <- matrix(...)).

每>是否有任何方法可以禁用环境窗格在RStudio中?似乎没有任何方法可以禁用环境窗格.

Per Is there any way to disable environment pane in RStudio? there doesn't seem to be any way of disabling the environment pane.

data.table仍然设法避免不必要的复制.试试:

data.table still manages to avoid unncessarily copies. Try:

library("data.table")
x <- as.data.table(matrix(c(11,21,31,12,22,32),nrow=3,ncol=2))
address(x)
x[2:3, `:=`(V1 = c(1, 1), V2 = c(8, 12))]
address(x)
x[, V3 := V1 + V2]
address(x)

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