如何从R应用函数访问全局/外部范围变量?

I can't seem to make apply function access/modify a variable that is declared outside... what gives?

我似乎无法使apply函数访问/修改一个在…到底发生了什么事?

    x = data.frame(age=c(11,12,13), weight=c(100,105,110))
    x

    testme <- function(df) {
        i <- 0
        apply(df, 1, function(x) {
            age <- x[1]
            weight <- x[2]
            cat(sprintf("age=%d, weight=%d\n", age, weight))
            i <- i+1   #this could not access the i variable in outer scope
            z <- z+1   #this could not access the global variable
        })
        cat(sprintf("i=%d\n", i))
        i
    }

    z <- 0
    y <- testme(x)
    cat(sprintf("y=%d, z=%d\n", y, z))

Results:

结果:

    age=11, weight=100
    age=12, weight=105
    age=13, weight=110
    i=0
    y=0, z=0

2 个解决方案

#1

Using the <<- operator you can write to variables in outer scopes:

使用<-运算符可以在外部作用域中对变量进行写入:

x = data.frame(age=c(11,12,13), weight=c(100,105,110))
x

testme <- function(df) {
    i <- 0
    apply(df, 1, function(x) {
        age <- x[1]
        weight <- x[2]
        cat(sprintf("age=%d, weight=%d\n", age, weight))
        i <<- i+1   #this could not access the i variable in outer scope
        z <<- z+1   #this could not access the global variable
    })
    cat(sprintf("i=%d\n", i))
    i
}

z <- 0
y <- testme(x)
cat(sprintf("y=%d, z=%d\n", y, z))

The result here:

结果:

age=11, weight=100
age=12, weight=105
age=13, weight=110
i=3
y=3, z=3

Note that the usage of <<- is dangerous, as you break up scoping. Do this only if really necessary and if you do, document that behavior clearly (at least in bigger scripts)

注意，使用<< <-是危险的，因为您要分解范围。只有在必要的时候才这样做，如果这样做了，就应该清楚地记录这种行为(至少在更大的脚本中)

#2

try the following inside your apply. Experiment with the value of n. I believe that for i it should be one less than for z.

在你的申请中试试下面的方法。实验n的值，我认为I应该比z小1。

         assign("i", i+1, envir=parent.frame(n=2))
         assign("z", z+1, envir=parent.frame(n=3))

---

testme <- function(df) {
    i <- 0
    apply(df, 1, function(x) {
        age <- x[1]
        weight <- x[2]
        cat(sprintf("age=%d, weight=%d\n", age, weight))

        ## ADDED THESE LINES
         assign("i", i+1, envir=parent.frame(2))
         assign("z", z+1, envir=parent.frame(3))

    })
    cat(sprintf("i=%d\n", i))
    i
}

OUTPUT

> z <- 0
> y <- testme(x)
age=11, weight=100
age=12, weight=105
age=13, weight=110
i=3
> cat(sprintf("y=%d, z=%d\n", y, z))
y=3, z=3