Add column_by_name() for RecordBatch

[wjones127]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

This is quite verbose:

let col: Option<ArrayRef> = record_batch.column(record_batch.schema().column_with_name("my_column")?.0)

Describe the solution you'd like

The simplest option is to add column_by_name() for RecordBatch. It is already implemented for StructArray.

let col: Option<ArrayRef> = record_batch.column_by_name("my_column")

But it might also be desirable to implement std::ops::Index for RecordBatch:

let col: Option<ArrayRef> = record_batch["my_column"]

Describe alternatives you've considered

Additional context

I was working with highly nested schemas with multiple levels of StructArrays in some unit tests, and it was a little annoying to access those deep fields. In an ideal world, I might be able to do something along the lines of:

let col: Option<ArrayRef> = record_batch["top_level_column"]?
    .as_struct_array()?["mid_level_column"]
    .as_struct_array()?["inner_column"];

This implies StructArray would implement Index in the same way that RecordBatch does. If we wanted to get fancy, it might not be crazy to implement this for ListArray or even MapArray.

[tustvold]

Makes sense to me

[askoa]

I'll pick this up.

Edit: I'll work on RecordBatch and StructArray. I am not planning to pick up ListArray and MapArray

[askoa]

I don't think we can return Option (or Result) from std::ops::Index. The trait function index returns a reference and hence cannot be a value created in the function. The function has to return reference to an item in self.

pub trait Index<Idx>
where
    Idx: ?Sized,
{
    type Output: ?Sized;

    fn index(&self, index: Idx) -> &Self::Output;
}

So the behavior of record_batch["name"] will be similar to record_batch.column(index).

Below are the return types I am planning. Let me know if you have alternate suggestion.

• column_by_name will return Option<&ArrayRef>
• column[name] will return &ArrayRef. The function will panic if the given name is not in the schema.

[ttencate]

This is done and can be closed, right?