[Rd] Subsetting the "ROW"s of an object

[Hervé Pagès]

Also the TRUEs cause problems if some dimensions are 0:

   > matrix(raw(0), nrow=5, ncol=0)[1:3 , TRUE]
   Error in matrix(raw(0), nrow = 5, ncol = 0)[1:3, TRUE] :
     (subscript) logical subscript too long

H.

On 06/08/2018 10:29 AM, Hadley Wickham wrote:
> I suspect this will have suboptimal performance since the TRUEs will
> get recycled. (Maybe there is, or could be, ALTREP, support for
> recycling)
> Hadley
> 
> On Fri, Jun 8, 2018 at 10:16 AM, Berry, Charles <ccberry using ucsd.edu> wrote:
>>
>>
>>> On Jun 8, 2018, at 8:45 AM, Hadley Wickham <h.wickham using gmail.com> wrote:
>>>
>>> Hi all,
>>>
>>> Is there a better to way to subset the ROWs (in the sense of NROW) of
>>> an vector, matrix, data frame or array than this?
>>
>>
>> You can use TRUE to fill the subscripts for dimensions 2:nd
>>
>>>
>>> subset_ROW <- function(x, i) {
>>>   nd <- length(dim(x))
>>>   if (nd <= 1L) {
>>>     x[i]
>>>   } else {
>>>     dims <- rep(list(quote(expr = )), nd - 1L)
>>>     do.call(`[`, c(list(quote(x), quote(i)), dims, list(drop = FALSE)))
>>>   }
>>> }
>>
>>
>> subset_ROW <-
>>      function(x,i)
>> {
>>      mc <- quote(x[i])
>>      nd <- max(1L, length(dim(x)))
>>      mc[seq(4, length=nd-1L)] <- rep(list(TRUE), nd - 1L)
>>      mc[["drop"]] <- FALSE
>>      eval(mc)
>>
>> }
>>
>>>
>>> subset_ROW(1:10, 4:6)
>>> #> [1] 4 5 6
>>>
>>> str(subset_ROW(array(1:10, c(10)), 2:4))
>>> #>  int [1:3(1d)] 2 3 4
>>> str(subset_ROW(array(1:10, c(10, 1)), 2:4))
>>> #>  int [1:3, 1] 2 3 4
>>> str(subset_ROW(array(1:10, c(5, 2)), 2:4))
>>> #>  int [1:3, 1:2] 2 3 4 7 8 9
>>> str(subset_ROW(array(1:10, c(10, 1, 1)), 2:4))
>>> #>  int [1:3, 1, 1] 2 3 4
>>>
>>> subset_ROW(data.frame(x = 1:10, y = 10:1), 2:4)
>>> #>   x y
>>> #> 2 2 9
>>> #> 3 3 8
>>> #> 4 4 7
>>>
>>
>> HTH,
>>
>> Chuck
>>
> 
> 
> 

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
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