Problem: Wrapping [.data.table seems to disable some print to console operations like head.
Question: Is there a way to modify [.blarg so that head(b) will print to console? Or do I need to write a print.blarg method or something similar?
Context: I'm trying to lightly extend data.table (see blarg) so that I can wrap [.data.table to identify and modify certain objects passed in j (a simplistic version of that is provided in [.blarg. This is occurring within an R-package development framework. I've included an example head.blarg function, but while this seems to work in a normal environment, it doesn't work as part of a package. See the bottom of the post for code to try out the package environment.
library('data.table')
blarg <- function(...){
r = data.table::data.table(...)
data.table::setattr(r, 'class', c('blarg', class(r)))
r
}
"[.blarg" <- function(x, i, j, by, ...){
mc <- match.call()
mc[[1]] <- quote(data.table:::`[.data.table`)
res = eval.parent(mc)
}
a = data.table(1:10)
b = blarg(1:10)
#Prints to console
head(a)
#> V1
#> 1: 1
#> 2: 2
#> 3: 3
#> 4: 4
#> 5: 5
#> 6: 6
#Does not print to console-- THIS IS THE PROBLEM BIT
head(b)
#But something is being returned
b1 <- head(b)
print(b1)
#> V1
#> 1: 1
#> 2: 2
#> 3: 3
#> 4: 4
#> 5: 5
#> 6: 6
#' Specifically provide a head definition modeled off of head.data.table
#' @noRd
#' @importFrom utils head
#' @exportS3Method
head.blarg <- function (x, n = 6L, ...)
{
#cat('blarg')
stopifnot(length(n) == 1L)
i = seq_len(if (n < 0L) max(nrow(x) + n, 0L) else min(n,
nrow(x)))
x[i, , ]
}
#This prints to console, but not when as part of a package
head(b)
#> V1
#> 1: 1
#> 2: 2
#> 3: 3
#> 4: 4
#> 5: 5
#> 6: 6
sessionInfo()
#> R version 4.1.1 (2021-08-10)
#> Platform: x86_64-w64-mingw32/x64 (64-bit)
#> Running under: Windows 10 x64 (build 19043)
#>
#> Matrix products: default
#>
#> locale:
#> [1] LC_COLLATE=English_United States.1252
#> [2] LC_CTYPE=English_United States.1252
#> [3] LC_MONETARY=English_United States.1252
#> [4] LC_NUMERIC=C
#> [5] LC_TIME=English_United States.1252
#>
#> attached base packages:
#> [1] stats graphics grDevices utils datasets methods base
#>
#> other attached packages:
#> [1] data.table_1.14.1
#>
#> loaded via a namespace (and not attached):
#> [1] ps_1.6.0 digest_0.6.27 withr_2.4.2 magrittr_2.0.1
#> [5] reprex_2.0.1 evaluate_0.14 highr_0.9 stringi_1.6.1
#> [9] rlang_0.4.11 cli_2.5.0 rstudioapi_0.13 fs_1.5.0
#> [13] rmarkdown_2.8 tools_4.1.1 stringr_1.4.0 glue_1.4.2
#> [17] xfun_0.23 yaml_2.2.1 compiler_4.1.1 htmltools_0.5.1.1
#> [21] knitr_1.33
As part of a package:
devtools::install_github('dcaseykc/headdtest')
source('https://raw.githubusercontent.com/dcaseykc/headdtest/main/exmple.R')
head(a) # Will print to console
head(b) # Probably won't print to console
After some more testing, changing [.blarg to explicitly return res seems to work.
"[.blarg" <- function(x, i, j, by, ...){
mc <- match.call()
mc[[1]] <- quote(data.table:::`[.data.table`)
res = eval.parent(mc)
return(res)
}