JoaoAparicio opened a new pull request, #412:
URL: https://github.com/apache/arrow-julia/pull/412
Currently we don't have the option to load just a subset of the columns.
This matters e.g. when compression is the bottleneck.
For example, create a compressed arrow file.
```julia
using Arrow
p = tempname();
N = 1000000
tbl = (
a=rand(N),
b=rand(N),
c=rand(N),
d=rand(N),
e=rand(N),
f=[rand(rand(0:100)) for _ in 1:N],
);
Arrow.write(p, tbl; compress=:zstd);
```
Column `f` is the longest - it has an expected 50*N elements vs N for the
rest Some times we only care for some of the other columns. Currently we must
decompress all columns regardless:
```julia
using BenchmarkTools
@btime tbl = Arrow.Table(p); # 359.205 ms (530 allocations: 794.23 MiB)
```
With this commit we can load only some of the columns
```julia
@btime tbl = Arrow.Table(p; filtercolumns=["a"]); # 6.146 ms (231
allocations: 14.33 MiB)
```
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