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Can you pass by reference with "R" ? for example, in the following code:
setClass("MyClass", representation( name="character" )) instance1 <-new("MyClass",name="Hello1") instance2 <-new("MyClass",name="Hello2") array = c(instance1,instance2) instance1 array instance1@name="World!" instance1 array the output is
> instance1 An object of class “MyClass” Slot "name": [1] "World!" > array [[1]] An object of class “MyClass” Slot "name": [1] "Hello1" [[2]] An object of class “MyClass” Slot "name": [1] "Hello2" but I wish it was
> instance1 An object of class “MyClass” Slot "name": [1] "World!" > array [[1]] An object of class “MyClass” Slot "name": [1] "World!" [[2]] An object of class “MyClass” Slot "name": [1] "Hello2" is it possible ?
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R passes everything by reference until you modify it. R creates a copy when you modify the object. You should always keep all the Object modifications in same function.
A mutable object's value can be changed when it is passed to a method. An immutable object's value cannot be changed, even if it is passed a new value. “Passing by value” refers to passing a copy of the value. “Passing by reference” refers to passing the real reference of the variable in memory.
Pass by reference (also called pass by address) means to pass the reference of an argument in the calling function to the corresponding formal parameter of the called function so that a copy of the address of the actual parameter is made in memory, i.e. the caller and the callee use the same variable for the parameter.
No.
Objects in assignment statements are immutable. R will copy the object not just the reference.
> v = matrix(1:12, nrow=4) > v [,1] [,2] [,3] [1,] 1 5 9 [2,] 2 6 10 [3,] 3 7 11 [4,] 4 8 12 > v1 = v > v1[,1] # fetch the first column [1] 1 2 3 4 (proviso: the statement above is true for R primitives, e.g., vectors, matrices), and also for functions; I cannot say for certain whether it's true for all R objects--just most of them, as well as the vast majority of the ones most often used.)
If you don't like this behavior you can opt out of it with the help from an R Package. E.g., there is an R Package called R.oo that allows you to mimic pass-by-reference behavior; R.oo is available on CRAN.
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Note that if you hope to use pass-by-reference simply to avoid the performance implications of copying an object that isn't modified (as is common in other languages with constant references), R does this automatically:
n <- 10^7 bigdf <- data.frame( x=runif(n), y=rnorm(n), z=rt(n,5) ) myfunc <- function(dat) invisible(with( dat, x^2+mean(y)+sqrt(exp(z)) )) myfunc2 <- function(dat) { x <- with( dat, x^2+mean(y)+sqrt(exp(z)) ) invisible(x) } myfunc3 <- function(dat) { dat[1,1] <- 0 invisible( with( dat, x^2+mean(y)+sqrt(exp(z)) ) ) } tracemem(bigdf) > myfunc(bigdf) > # nothing copied > myfunc2(bigdf) > # nothing copied! > myfunc3(bigdf) tracemem[0x6e430228 -> 0x6b75fca0]: myfunc3 tracemem[0x6b75fca0 -> 0x6e4306f0]: [<-.data.frame [<- myfunc3 tracemem[0x6e4306f0 -> 0x6e4304f8]: [<-.data.frame [<- myfunc3 > > library(microbenchmark) > microbenchmark(myfunc(bigdf), myfunc2(bigdf), myfunc3(bigdf), times=5) Unit: milliseconds expr min lq median uq max 1 myfunc2(bigdf) 617.8176 641.7673 644.3764 683.6099 698.1078 2 myfunc3(bigdf) 1052.1128 1134.0822 1196.2832 1202.5492 1206.5925 3 myfunc(bigdf) 598.9407 622.9457 627.9598 642.2727 654.8786 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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