r - 检查 data.table 是否在函数中键入，R

Question

我想检查data.table我的函数正在运行的 a 是否已key编辑。如何做到这一点？例如：

x = data.table(a=1:100, b=100:1)
setkey(x, a)
f = function(v) {v+1}
x[,f(b),by=a]

我想检查一下里面 f是否设置了钥匙x以及那key是什么

f在这种情况下，这将需要访问从中调用的对象x。这可能data.table吗？

Answer 1

f = function(v) {
    cat("haskey(caller's x) is",eval(quote(haskey(x)), sys.frame(2)),"\n")
    # x in line above = name of first argument to `[.data.table`
    v+1
}
DT = data.table(a=1:3,foo=1:6)
DT[,f(foo),by=a]
haskey(caller's x) is FALSE 
haskey(caller's x) is FALSE 
haskey(caller's x) is FALSE 
   a V1
1: 1  2
2: 1  5
3: 2  3
4: 2  6
5: 3  4
6: 3  7

setkey(DT,a)
DT[,f(foo),by=a]
haskey(caller's x) is TRUE 
haskey(caller's x) is TRUE 
haskey(caller's x) is TRUE 
   a V1
1: 1  2
2: 1  5
3: 2  3
4: 2  6
5: 3  4
6: 3  7
>

但是你为什么需要那个？