Row group reading support?

[cornhundred]

Hi, thanks for the library it has been very useful for us. Is it possible to read specific row groups using search criteria (predicate pushdown I think it is called)? We're testing the use of parquet files for tiling spatial biology data. But it would be cool to be able to have one big file instead of lots of small files that could serve the same purpose.

[kylebarron]

You can specify row group indexes in the ReaderOptions: https://kylebarron.dev/parquet-wasm/types/esm_parquet_wasm.ReaderOptions.html

[cornhundred]

Thanks, is it possible to query the metadata for the row groups first to determine which row groups need to be loaded? I'm thinking that could be done once and then referenced whenever new row groups are needed.

[kylebarron]

You can use ParquetFile to access the ParquetMetaData and then iterate through the metadata of all row groups. That should probably give you enough of what you need