使用与列同名的变量对 data.table 进行子集 [英] Subsetting data.table using variables with same name as column

问题描述

我想使用一个与导致一些问题的列同名的变量对 data.table 进行子集化:

I want to subset a data.table using a variable which has the same name as the column which leeds to some problems:

dt <- data.table(a=sample(c('a', 'b', 'c'), 20, replace=TRUE),
                 b=sample(c('a', 'b', 'c'), 20, replace=TRUE),
                 c=sample(20), key=c('a', 'b'))

evn <- environment()
a <- 'b'
dt[a == a]

#Expected Result
dt[a == 'b']

我遇到了这个可能的解决方案:

env <- environment()
dt[a == get('a',env)]

但它并不方便:

this.a = a
dt[a == this.a]

那么还有其他优雅的解决方案吗?

So is there another elegant solution?

推荐答案

目前，一个临时的解决方案可能是，

For now, a temporary solution could be,

`..` <- function (..., .env = globalenv())
{
  get(deparse(substitute(...)), env = .env)
}

..(a)
## [1] "b"

dt[a==..(a)]
##    a b  c
## 1: b a 15
## 2: b a 11
## 3: b b  8
## 4: b b  4
## 5: b c  5
## 6: b c 12

虽然这看起来很优雅，但我仍在等待针对此类范围问题的更强大的解决方案.

Though this looks elegant, I am still waiting for a more robust solution to such scope issues.

根据@mnel 的建议编辑，

Edited according to @mnel's suggestion,

`..` <- function (..., .env = sys.parent(2))
{
  get(deparse(substitute(...)), env = .env)
}

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