R：深拷贝函数参数 [英] R: deep copy a function argument

问题描述

考虑以下code

  I = 3
J =
我= 4＃J 1 = I
 

不过，我要的是

  I = 3
F＆下;  - 功能（t，J =ⅰ）
    X *Ĵ
I = 4
F（4）＃16，但我希望它是12
 

如果你想知道为什么我想这样做，你可以考虑这个code - 应用程序是一个多递减模型。一个转移矩阵的对角线是该行中的其他递减的总和。我想定义我需要比计算使用这些递减的其他功能递减。在这种情况下，我只需要uxt01和uxt10并从这些欲产生uxt00和uxt11的功能。我想要的东西，扩展到更高的层面。

  QXT＆LT;  - 矩阵（C（uxt00 =功能（T = 0，X = 0）0，
                uxt01 =函数（t = 0时，X = 0）0.05，
                uxt10 =函数（t = 0时，X = 0）0.07
                uxt11 =函数（t = 0时，X = 0）0），2，2，byrow = TRUE）Qxt.diag＆LT;  - 功能（QXT）{
    ndecrements＆LT;  - 长度（QXT [1]）
    对（序列（1索引，N，N + 1））{＃1，4
        QXT [指数]＆LT;  - 功能（T = 0，X = 0，I =指数，N = ndecrements）{
            行＆LT;  - 上限（索引/ ndecr）
            row.decrements＆下;  - 序列（（行 -  1）* N + 1，（行）* N）
            other.decrements＆LT;  -  row.decrements [！这（row.decrements = I]
            -sum（不公开（lapply（Qxt.fns [other.decrements]，
                功能（F）F（T，X））））
        }
    }
    Qxt.fns
}
 

解决方案

这可以通过为正式参数分配默认前pression做Ĵ手动，在创建功能之后：

  I＆LT;  -  3;
F＆LT;  - 函数（X，J）X *焦耳;
F;
##功能（X，j）的X *Ĵ
甲醛（F）;
## $ X
##
##
##附加$ J
##
##
甲醛（F）$ J＆LT;  - 我;
F;
##功能（t，J = 3）
## X *Ĵ
甲醛（F）;
## $ X
##
##
##附加$ J
## [1] 3
##
I＆LT;  -  4;
F（4）;
## [1] 12
 

这是唯一可能的，因为R是一个真棒语言，为您提供的功能，所有这三个特殊的性质，这是完整的读/写访问：

1. 的语法树，它包括身体：<一href=\"https://stat.ethz.ch/R-manual/R-devel/library/base/html/body.html\"><$c$c>body().


2. 形式参数和它们的默认值（这本身解析树）：<一href=\"https://stat.ethz.ch/R-manual/R-devel/library/base/html/formals.html\"><$c$c>formals().


3. 的封闭环境（这是用来实现闭包）：<一href=\"https://stat.ethz.ch/R-manual/R-devel/library/base/html/environment.html\"><$c$c>environment().

Consider the following code

i = 3
j = i
i = 4 # j != i

However, what I want is

i = 3
f <- function(x, j=i) 
    x * j
i = 4
f(4) # 16, but i want it to be 12

In case you are wondering why I want to do this you could consider this code - the application is a multiple decrements model. The diagonals of a transition matrix are the sum of the other decrements in that row. I would like to define the decrements I need than calculate the other functions using those decrements. In this case, I only need uxt01 and uxt10 and from these I want to produce the functions uxt00 and uxt11. I wanted something that scales to higher dimensions.

Qxt <- matrix(c(uxt00=function(t=0,x=0) 0,
                uxt01=function(t=0,x=0) 0.05,
                uxt10=function(t=0,x=0) 0.07
                uxt11=function(t=0,x=0) 0), 2, 2, byrow=TRUE)

Qxt.diag <- function(Qxt) {
    ndecrements <- length(Qxt[1,])
    for(index in seq(1, N, N+1)) { # 1, 4
        Qxt[[index]] <- function(t=0, x=0, i=index, N=ndecrements) {
            row <- ceiling(index/ndecr)
            row.decrements <- seq( (row - 1)*N + 1, (row)*N) 
            other.decrements <- row.decrements[which(row.decrements != i]
            -sum(unlist(lapply(Qxt.fns[[other.decrements]], 
                function(f) f(t,x))))
        }
    }
    Qxt.fns
}

解决方案

This can be done by assigning the default expression for the formal parameter j manually, after creating the function:

i <- 3;
f <- function(x,j) x*j;
f;
## function(x,j) x*j
formals(f);
## $x
##
##
## $j
##
##
formals(f)$j <- i;
f;
## function (x, j = 3)
## x * j
formals(f);
## $x
##
##
## $j
## [1] 3
##
i <- 4;
f(4);
## [1] 12

This is only possible because R is an awesome language and provides you complete read/write access to all three special properties of functions, which are:

1. The parse tree that comprises the body: body().
2. The formal parameters and their default values (which are themselves parse trees): formals().
3. The enclosing environment (which is used to implement closures): environment().

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