rluvaton opened a new issue, #6846:
URL: https://github.com/apache/arrow-rs/issues/6846
**Which part is this question about**
library api
**Describe your question**
I have a `ListArray` and I want to filter each item in the list
```text
┌─────────────┐ -> ┌─────────────┐
│ [A,B,C] │ -> │ [A,C] │
├─────────────┤ -> ├─────────────┤
│ [] │ -> │ [] │
├─────────────┤ -> ├─────────────┤
│ NULL │ -> │ NULL │
├─────────────┤ -> ├─────────────┤
│ [D] │ -> │ [] │
├─────────────┤ -> ├─────────────┤
│ [NULL, F] │ -> │ [NULL, F] │
└─────────────┘ -> └─────────────┘
```
But I couldn't find a way to do it
I tried this:
```rust
#[cfg(test)]
mod tests {
use arrow::array::{Array, BooleanArray, ListArray};
use arrow::datatypes::Int32Type;
use arrow::error::ArrowError;
use std::ops::Deref;
#[test]
fn list_array() -> Result<(), ArrowError> {
// Create list
let list_array = create_list_for_test();
// go over each list in the array and filter items in it
let new_list: ListArray = list_array
.iter()
.map(|x| {
match x {
None => Ok(None),
Some(x) => {
let some_predicate =
BooleanArray::from((0..x.len()).map(|i| i % 2 == 0).collect::<Vec<_>>());
let val = arrow::compute::filter(x.deref(),
&some_predicate)?;
Ok(Some(val))
}
}
})
.collect::<Result<_, _>>()?;
println!("{:?}", new_list);
Ok(())
}
// This can be list of list of int32 or any other inner list type
fn create_list_for_test() -> ListArray {
let data = vec![
Some(vec![Some(0), Some(1), Some(2)]),
None,
Some(vec![Some(3), None, Some(5)]),
Some(vec![Some(6), Some(7)]),
];
let list_array = ListArray::from_iter_primitive::<Int32Type, _,
_>(data);
list_array
}
}
```
But got:
```
error[E0277]: a value of type `GenericListArray<i32>` cannot be built from
an iterator over elements of type `Option<Arc<dyn arrow::array::Array>>`
--> arrow-pg/src/lib.rs:31:24
|
31 | .collect::<Result<_, _>>()?;
| ------- ^^^^^^^^^^^^ value of type
`GenericListArray<i32>` cannot be built from
`std::iter::Iterator<Item=Option<Arc<dyn arrow::array::Array>>>`
| |
| required by a bound introduced by this call
|
= help: the trait `FromIterator<Option<Arc<dyn arrow::array::Array>>>`
is not implemented for `GenericListArray<i32>`, which is required by `Result<_,
_>: FromIterator<Result<Option<Arc<dyn arrow::array::Array>>, _>>`
= help: the trait `FromIterator<Result<A, E>>` is implemented for
`Result<V, E>`
= note: required for `Result<GenericListArray<i32>, _>` to implement
`FromIterator<Result<Option<Arc<dyn arrow::array::Array>>, _>>`
note: required by a bound in `collect`
-->
/Users/something/.rustup/toolchains/1.80-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:2001:19
|
2001 | fn collect<B: FromIterator<Self::Item>>(self) -> B
| ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in
`Iterator::collect`
```
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