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# Table$to\_arrow\_batch\_reader

### Table$<mark style="color:purple;">to\_arrow\_batch\_reader</mark>(max\_results=NULL, variables=NULL) →  [RecordBatchReader](#class-recordbatchreader)

Returns a reader that mimics the [Arrow RecordBatchStreamReader](https://arrow.apache.org/docs/dev/r/reference/RecordBatchReader.html), which can then be consumed to process batches of rows in a streaming fashion. By streaming data, you can avoid the need to load more than a small chunk of data into memory at a time. This approach is highly scalable, since it won't be limited by available memory or disk.

The batch reader exposes a `$read_next_batch()` method, which should be repeatedly called to fetch the next [Arrow RecordBatch](https://arrow.apache.org/docs/dev/r/reference/RecordBatch.html). If next() returns `NULL`, this signals that there is no more data left to read.

{% hint style="info" %}
Also callable on [Queries](/api/client-libraries/redivis-r/reference/query.md) and [Uploads](/api/client-libraries/redivis-r/reference/upload.md) →&#x20;

 `query$to_arrow_batch_reader(...)` | `upload$to_arrow_batch_reader(...)`
{% endhint %}

### **Parameters:**

**`max_results` :&#x20;*****int, default NULL***\
The max number of records to load into the dataframe. If not specified, the entire table will be loaded.

**`variables` :&#x20;*****list(str)*****&#x20;|&#x20;*****character vector*** \
The specific variables to return, e.g., `variables = c("name", "date")` . If not specified, all variables in the table will be returned.

### **Returns:**&#x20;

#### **class RecordBatchReader()**

***Methods*****:**

`$read_next_batch()`→ [Arrow RecordBatch](https://arrow.apache.org/docs/dev/r/reference/RecordBatch.html) | NULL\
Read the next batch of records. If `NULL` is returned, indicates that there is nothing left to read.

`$close()`→ void\
Close the underlying connection and releases all resources.

### Notes:

The returned instance largely mirrors the behavior of the [Arrow RecordBatchStreamReader](https://arrow.apache.org/docs/dev/r/reference/RecordBatchReader.html), though only the `$read_next_batch()` method is implemented.

Make sure to call `on.exit(batch_reader$close())` to ensure resources are released if your application prematurely exits.

### Examples

```r
batch_reader = redivis$table("test_scores")$to_arrow_batch_reader()

# Make sure the batch_reader gets closed when we exit this function,
# including if an error occurs
on.exit(batch_reader$close())

count <- 0
total <- 0

# Streaming works especially well when performing various aggregations
while (!is.null(batch <- reader$read_next_batch())){
  # batch is an instance of an Arrow RecordBatch -> https://arrow.apache.org/docs/r/reference/record_batch.html
  scores <- batch$scores
  count <- count + length(scores)
  total <- sum(scores)
}

print(str_interp("The average of all test cores was ${total/count}"))
```


---

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