DataFrame.info

[ueshin]

Implement DataFrame.info.

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.info.html
memory usage is not needed for Koalas.

[burakyilmaz321]

Hi @ueshin ! I was thinking about how to implement this in spark. I think null counts would be problematic since counting (and printing) nulls for every column is quite expensive in spark. Any suggestion here? Besides, I can start working on this and send a PR that adds a method to koalas.DataFrame

[HyukjinKwon]

@burakyilmaz321 please go ahead for other APIs. For this API, I think we can calculate via using Pyspark API (e.g., select(count(column.isNotNull)))`