> But I can't figure out how to express "select struct field 0 from field 2
> of the original table where field 2 is a struct column"
>
> Any idea how the substrait message should look like for the above?
I believe it would be:
```
"expression": {
"selection": {
"direct_reference": {
"struct_field" {
"field": 2,
"child" {
"struct_field" { "field": 0 }
}
}
}
"root_reference": { }
}
}
```
To get the above I used the following python (requires [1] which could use
a review and you need some way to convert the binary substrait to json, I
used a script I have lying around):
```
>>> import pyarrow as pa
>>> import pyarrow.compute as pc
>>> schema = pa.schema([pa.field("points", pa.struct([pa.field("x",
pa.float64()), pa.field("y", pa.float64())]))])
>>> expr = pc.field(("points", "x"))
>>> expr.to_substrait(schema)
<pyarrow.Buffer address=0x5602249c9970 size=92 is_cpu=True is_mutable=False>
```
[1] https://github.com/apache/arrow/pull/34834
On Tue, Aug 1, 2023 at 1:45 PM Li Jin <ice.xell...@gmail.com> wrote:
> Hi,
>
> I am recently trying to do
> (1) assign a struct type column s<v1, v2>
> (2) flatten the struct columns (by assign v1=s[v1], v2=s[v2] and drop the s
> column)
>
> via Substrait and Acero.
>
> However, I ran into the problem where I don't know the proper substrait
> message to encode this (for (2))
>
> Normally, if I select a column from the origin table, it would look like
> this (e.g, select column index 1 from the original table):
>
> selection {
> direct_reference {
> struct_field {
> 1
> }
> }
> }
>
> But I can't figure out how to express "select struct field 0 from field 2
> of the original table where field 2 is a struct column"
>
> Any idea how the substrait message should look like for the above?
>
