有没有一种方法可以防止在修改属性时进行修改时复制?

问题描述

我很惊讶用下面的代码制作了矩阵的副本:

I am surprised that a copy of the matrix is made in the following code:

> (m <- matrix(1:12, nrow = 3))
     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12
> tracemem(m)
[1] "<000001E2FC1E03D0>"
> str(m)
 int [1:3, 1:4] 1 2 3 4 5 6 7 8 9 10 ...
> attr(m, "dim") <- 4:3
tracemem[0x000001e2fc1e03d0 -> 0x000001e2fcb05008]: 
> m
     [,1] [,2] [,3]
[1,]    1    5    9
[2,]    2    6   10
[3,]    3    7   11
[4,]    4    8   12
> str(m)
 int [1:4, 1:3] 1 2 3 4 5 6 7 8 9 10 ...

有用吗?可以避免吗?

我的结果与GKi不同.

I do not have the same results as GKi.

> sessionInfo()
R version 4.0.3 (2020-10-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19041)

Matrix products: default

locale:
[1] LC_COLLATE=French_France.1252  LC_CTYPE=French_France.1252    LC_MONETARY=French_France.1252
[4] LC_NUMERIC=C                   LC_TIME=French_France.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_4.0.3 tools_4.0.3   
> m <- matrix(1:12, nrow = 3)
> tracemem(m)
[1] "<000001F8DB2C7D90>"
> attr(m, "dim") <- c(4, 3)
tracemem[0x000001f8db2c7d90 -> 0x000001f8db2d93f0]: 

一个区别是我不使用BLAS库...

One difference is that I do not use BLAS library...

推荐答案

我正在使用R 3.6.3，实际上已经制作了一个副本.要更改属性而不进行复制，可以使用 data.table 包的 setattr 函数:

I'm using R 3.6.3 and indeed a copy is made. To change an attribute without making a copy, you can use the setattr function of the data.table package:

library(data.table)

m <- matrix(1:12, nrow = 3)
.Internal(inspect(m))

setattr(m, "dim", c(4L,3L))
.Internal(inspect(m))

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