altrepr

altrepr shines light on the mysterious ALTREP objects in R.

It offers:

Inspection of ALTREP types
Specialized constructors and inspections for the 4 built-in ALTREP classes in R
Detailed vignettes that explore these classes, how to use them in R, and their internal workings

Installation

You can install the development version of altrepr like so:

remotes::install_github("multimeric/altrepr")

Example

library(altrepr)

1:5 is just a normal integer vector right? Wrong! It’s a sneaky ALTREP masquerading as an integer vector.

x <- 1:5
is_altrep(x)
#> [1] TRUE

We can dig into the details:

alt_details(x)
#> $class_name
#> [1] "compact_intseq"
#> 
#> $pkg_name
#> [1] "base"
#> 
#> $base_type
#> [1] "integer"
#> 
#> $data1
#> [1] 5 1 1
#> 
#> $data2
#> NULL

compact_details(x)
#> $length
#> [1] 5
#> 
#> $start
#> [1] 1
#> 
#> $step
#> [1] 1
#> 
#> $expanded
#> NULL

And, if we’re feeling brave, we can even edit the ALTREP:

set_alt_data1(x, c(10, 1, 1))
x
#>  [1]  1  2  3  4  5  6  7  8  9 10

For more information, refer to the detailed vignettes!