perf: faster standalone compact

[m-muecke]

compact1 <- function(x) Filter(length, x)
compact2 <- function(x) x[as.logical(lengths(x))]
compact3 <- function(x) x[lengths(x) > 0L]

x <- list(1:100, NULL, NULL, NULL, 1:100)
bench::mark(
  compact1(x),
  compact2(x),
  compact3(x),
  iterations = 100
)
#> # A tibble: 3 × 6
#>   expression       min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr>  <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 compact1(x)   2.91µs   3.28µs    13534.        0B        0
#> 2 compact2(x) 491.97ns 574.04ns   115615.        0B        0
#> 3 compact3(x) 492.03ns 574.04ns   138659.        0B        0

^{Created on 2025-01-23 with reprex v2.1.1}

[lionel-]

Thanks!