R: += (plus equals) and ++ (plus plus) equivalent from c++/c#/java, etc.?

Does R have a concept of 开发者_JAVA百科+= (plus equals) or ++ (plus plus) as c++/c#/others do?

No, it doesn't, see: R Language Definition: Operators

Following @GregaKešpret you can make an infix operator:

`%+=%` = function(e1,e2) eval.parent(substitute(e1 <- e1 + e2))
x = 1
x %+=% 2 ; x

R doesn't have a concept of increment operator (as for example ++ in C). However, it is not difficult to implement one yourself, for example:

inc <- function(x)
{
 eval.parent(substitute(x <- x + 1))
}

In that case you would call

x <- 10
inc(x)

However, it introduces function call overhead, so it's slower than typing x <- x + 1 yourself. If I'm not mistaken increment operator was introduced to make job for compiler easier, as it could convert the code to those machine language instructions directly.

R doesn't have these operations because (most) objects in R are immutable. They do not change. Typically, when it looks like you're modifying an object, you're actually modifying a copy.

Increment and decrement by 10.

require(Hmisc)
inc(x) <- 10 

dec(x) <- 10

We released a package, roperators, to help with this kind of thing. You can read more about it here: https://happylittlescripts.blogspot.com/2018/09/make-your-r-code-nicer-with-roperators.html

install.packages('roperators')
require(roperators)

x <- 1:3
x %+=% 1; x
x %-=% 3; x
y <- c('a', 'b', 'c')
y %+=% 'text'; y
y %-=% 'text'; y

# etc

We can override +. If unary + is used and its argument is itself an unary + call, then increment the relevant object in the calling environment.

`+` <- function(e1,e2){
  # if binary `+`, keep original behavior
  if(!missing(e2)) return(base::`+`(e1, e2))
  
  # if inner call isn't unary `+` called on language object,
  # keep original behavior
  inner_call <- substitute(e1)
  inner_call_is_plus_on_lng <-
    length(inner_call) == 2 &&
    identical(inner_call[[1]], quote(`+`)) &&
    is.language(inner_call[[2]])
  if(!inner_call_is_plus_on_lng) return(base::`+`(e1))
  
  eval.parent(substitute(X <- X + 1, list(X = inner_call[[2]])))
}

x <- 10

++x
x
#> [1] 11

other operations don't change :

x + 2
#> [1] 13
x ++ 2
#> [1] 13
+x
#> [1] 11
x
#> [1] 11

I can't really recommend it since you're messing with primitives which are optimised for a reason.

We can also use inplace

library(inplace)
x <- 1
x %+<-% 2

If you want to use i++ in an array to increment the index, you can try i <- i + 1, for example,

k = 0
a = 1:4
for (i in 1:4) 
    cat(a[k <- k + 1], " ")
# 1 2 3 4

but here <- can NOT be replaced with =, which does not update the index,

k = 0
a = 1:4
for (i in 1:4) 
    cat(a[k = k + 1], " ")
# 1 1 1 1

since = and <- are not always equivalent, as said in ?`<-`