R:如何使用data.table的函数输入创建函数 [英] R: How can I make a function with a function input with data.table
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问题描述
我在使用data.table执行时遇到问题。这是我的问题。我写了一个简单的减法函数:
I faced a problem when exercising with data.table. Here is my problem. I wrote a simple subtraction function:
minus <- function(a, b){
return(a - b)
}
我的数据集是一个简单的data.table:
My dataset is a simple data.table:
dt <- as.data.table(data.frame(first=c(5, 6, 7), second=c(1,2,3)))
dt
first second
1 5 1
2 6 2
3 7 3
我想写另一个函数,
myFunc <- function(dt, FUN, ...){
return(dt[, new := FUN(...)])
}
用法简单:
res <- myFunc(dt, minus, first, second)
,结果如下: p>
and the result would be the following:
res
first second new
1: 5 1 4
2: 6 2 4
3: 7 3 4
如何归档这样的目标?谢谢!
How can I archive such a goal? Thanks!
推荐答案
也许有更好的方法,但你可以尝试这样:
Maybe there's a better way, but you can try something like this:
myFunc <- function(indt, FUN, ...) {
FUN <- deparse(substitute(FUN)) # Get FUN as a string
FUN <- match.fun(FUN) # Match it to an existing function
dots <- substitute(list(...))[-1] # Get the rest of the stuff
# I've used `copy(indt)` so that it doesn't affect your original dataset
copy(indt)[, new := Reduce(FUN, mget(sapply(dots, deparse)))][]
}
(注意这是非常明确的,
(Note that this is very specific to how you've created your minus()
function.)
这里是操作中:
res <- myFunc(dt, minus, first, second)
dt ## Unchanged
# first second
# 1: 5 1
# 2: 6 2
# 3: 7 3
res
# first second new
# 1: 5 1 4
# 2: 6 2 4
# 3: 7 3 4
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