tustvold commented on issue #4908:
URL: https://github.com/apache/arrow-rs/issues/4908#issuecomment-1771007863
> Re-ordering columns
Casting from
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Int32, false),
])
```
To
```
DataType::Struct(Fields::new(vec![
Field::new("b", DataType::Int32, false),
Field::new("a", DataType::Int32, false),
])
```
> Adding new nullable fields by adding entirely null columns as appropriate
Casting from
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Int32, false),
])
```
To
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Int32, false),
Field::new("c", DataType::Int32, true),
])
```
> Casting columns within the array
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Int32, false),
])
```
To
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, true),
Field::new("b", DataType::Int64, false),
])
```
> We should support combinations of:
So the eventual goal would be to support
```
DataType::Struct(Fields::new(vec![
Field::new("a", DataType::Int32, false),
Field::new("b", DataType::Int32, false),
])
```
To
```
DataType::Struct(Fields::new(vec![
Field::new("c", DataType::Float32, true),
Field::new("b", DataType::Int64, false),
Field::new("a", DataType::Int32, false),
])
```
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