any good library support load/write data to disc available? e.g. pandas has support to write feather format (I use a lot) or hdf5 file (I use a lot too), I search around for few days, seems could not find any. thought gonna have some library support feather format as it is from Apache Arrow ....

Quoting https://github.com/apache/arrow/issues/2240:

Feather in its current form should be considered deprecated. Writing the Arrow file format from Java is already supported

So as far as I have seen feather format is neither supported by Java nor Kotlin, but as Arrow format is supported by Java, you can use it from Kotlin too, like any other Java library. Generally I'd use

kotlinx.serialization

though to write and read data. It supports JSON, CBOR and ProtoBuf natively and that are also community support modules for other formats like XML or YAML.

Thanks @Vampire I'll take a look Java hdf5, reason mention these two formats was try to communicate with Python, as of now, charting in Kotlin is not ready, so large amount of data (timeseries) will be produced by Kotlin and loaded into Python to analyze/visualize. As of now, I am using csv. Just loading time is slower, in Python, load feather format is really fast and convenient, if not available, or if try to package a lot info into single file, i usually go with hdf5.