mean.piar_index() is slow for large indexes

[marberts]

Aggregating an index over subperiods seems slow given that it should be a simple operation. The constraint appears to be the loop.

bench::press(
  levels = c(1e2, 1e3, 1e4),
  periods = c(3, 12, 120),
  {
    index <- as_index(matrix(runif(levels * periods), levels))
    bench::mark(mean(index), min_iterations = 10)
  }
)

  expression levels periods      min   median `itr/sec` mem_alloc `gc/sec` n_itr  n_gc total_time 
  <bch:expr>  <dbl>   <dbl> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl> <int> <dbl>   <bch:tm> 
1 mean(inde…    100       3   1.05ms   1.18ms   727.       8.81KB     7.35   297     3   408.44ms 
2 mean(inde…   1000       3   7.69ms   8.87ms   113.      79.06KB     7.90    43     3   379.68ms 
3 mean(inde…  10000       3  74.34ms  75.09ms    13.3    881.56KB    31.1      3     7   225.18ms 
4 mean(inde…    100      12   3.48ms   3.96ms   252.      25.83KB    10.8     93     4   369.46ms 
5 mean(inde…   1000      12  30.57ms  31.63ms    31.2    233.09KB     9.35    10     3   320.98ms 
6 mean(inde…  10000      12  338.2ms 398.73ms     2.42      2.5MB     7.74    10    32      4.14s 
7 mean(inde…    100     120  35.56ms  39.78ms    25.0    233.06KB    10.7      7     3   279.66ms 
8 mean(inde…   1000     120  389.5ms 415.32ms     2.44     2.04MB     6.34    10    26       4.1s 
9 mean(inde…  10000     120    4.19s    8.93s     0.116   22.12MB     3.82    10   329      1.44m 

[marberts]

These timings have improved a bit over the last year.

  levels periods      min   median mem_alloc n_itr
   <dbl>   <dbl> <bch:tm> <bch:tm> <bch:byt> <int>
1    100       3 473.32µs 504.85µs   11.44KB   921
2   1000       3   2.68ms   2.96ms  102.78KB   154
3  10000       3  25.28ms  26.86ms    1.09MB    14
4    100      12 685.86µs 746.54µs   19.31KB   623
5   1000      12   4.87ms   5.22ms  173.94KB    84
6  10000      12  47.56ms   49.9ms    1.78MB     6
7    100     120   3.35ms   3.63ms  218.22KB   123
8   1000     120  31.68ms  32.99ms    1.97MB    10
9  10000     120  339.1ms 356.81ms   19.65MB    10