[GitHub] [arrow] jorgecarleitao commented on a change in pull request #9293: ARROW-11349: [Rust] Add from_iter_values to create arrays from (non null) values

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jorgecarleitao commented on a change in pull request #9293:
URL: https://github.com/apache/arrow/pull/9293#discussion_r563148896



##########
File path: rust/arrow/src/array/array_primitive.rs
##########
@@ -94,6 +94,32 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
         let offset = i + self.offset();
         unsafe { *self.raw_values.as_ptr().add(offset) }
     }
+
+    /// Creates a PrimitiveArray based on an iterator of values without nulls
+    pub fn from_iter_values<I: IntoIterator<Item = T::Native>>(iter: I) -> Self {
+        let iter = iter.into_iter();
+        let (_, data_len) = iter.size_hint();
+        let data_len = data_len.expect("Iterator must be sized"); // panic if no upper bound.
+
+        let mut val_buf = MutableBuffer::new(
+            data_len * mem::size_of::<<T as ArrowPrimitiveType>::Native>(),
+        );
+
+        iter.for_each(|item| {
+            val_buf.push(item);
+        });

Review comment:
       Yes, that is what I meant: it should now be possible to do
   
   ```rust
   let values = vec![0i32, 1];
   
   let values = values.iter().map(|x| x + 1);
   
   let buffer: Buffer: values.collect();
   ```
   
   wrt to the `len`: that is a good point that I have had not thought about. 👍 
   
   One option is to do what you wrote. Another could be (I haven't tried to compile this, as `Fn` could become `FnMut`):
   
   ```
   let mut count = 0;
   let iter = iter.map(|x| {
      count += 1;
   x
   });
   ```
   
   I would probably have taken your idea, though :)
   




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