r语言 - 返回数据的副本.表从ReferenceClass方法

Question

我尝试从ReferenceClass的方法返回data.table s的副本:

dummy <- setRefClass(
  "dummy",
  fields = list(
    dt = "data.table"
  ),
  methods = list(
    initialize = function( df ){
      if( !missing( df ) ){
        dt <<- data.table( df , key = "a" )
      }
    },
    getTab = function( ix ){
      return( copy(dt[ ix, ]) )
    }
  )
)

然而，调用dummy$getTab()会产生一个我不理解的错误:

d <- dummy$new( data.frame( a = 1:10, b = 1:10 ) )
d$getTab( 2:5 )
Error in if (shallow) assign(field, get(field, envir = selfEnv), envir = vEnv) else { : 
  argument is not interpretable as logical
In addition: Warning message:
In if (shallow) assign(field, get(field, envir = selfEnv), envir = vEnv) else { :
 the condition has length > 1 and only the first element will be used

我没有线索，这是什么意思，这是从哪里来的。另外，下面两个过程可以正常工作，没有任何问题:

copy( d$dt[ 2:5 ] )
mycopy <- function( dt, ix ) {
  return( copy(dt[ ix, ]) )
}
mycopy( d$dt, 2:5 )

Answer 1

好的，对不起，这是一个愚蠢的错误，我只是监督了envRefClass$copy()方法。因此，解决方案是显式地调用data.table::copy:

dummy <- setRefClass(
  "dummy",
  fields = list(
    dt = "data.table"
  ),
  methods = list(
    initialize = function( df ){
      if( !missing( df ) ){
        dt <<- data.table( df , key = "a" )
      }
    },
    getTab = function( ix ){
      return( data.table::copy(dt[ ix, ]) )
    }
  )
)