polars.DataFrame.iter_slices#

DataFrame.iter_slices( n_rows: int = 10000, ) → Iterator[DataFrame][source]#

Returns a non-copying iterator of slices over the underlying DataFrame.

Parameters:

n_rows: Determines the number of rows contained in each DataFrame slice.

See also

iter_rows: Row iterator over frame data (does not materialise all rows).
partition_by: Split into multiple DataFrames, partitioned by groups.

Examples

>>> from datetime import date
>>> df = pl.DataFrame(
...     data={
...         "a": range(17_500),
...         "b": date(2023, 1, 1),
...         "c": "klmnoopqrstuvwxyz",
...     },
...     schema_overrides={"a": pl.Int32},
... )
>>> for idx, frame in enumerate(df.iter_slices()):
...     print(f"{type(frame).__name__}:[{idx}]:{len(frame)}")
DataFrame:[0]:10000
DataFrame:[1]:7500

Using iter_slices is an efficient way to chunk-iterate over DataFrames and any supported frame export/conversion types; for example, as RecordBatches:

>>> for frame in df.iter_slices(n_rows=15_000):
...     record_batch = frame.to_arrow().to_batches()[0]
...     print(f"{record_batch.schema}\n<< {len(record_batch)}")
a: int32
b: date32[day]
c: large_string
<< 15000
a: int32
b: date32[day]
c: large_string
<< 2500