# databricks.koalas.DataFrame.spark.coalesce¶

spark.coalesce(num_partitions: int) → ks.DataFrame

Returns a new DataFrame that has exactly num_partitions partitions.

Note

This operation results in a narrow dependency, e.g. if you go from 1000 partitions to 100 partitions, there will not be a shuffle, instead each of the 100 new partitions will claim 10 of the current partitions. If a larger number of partitions is requested, it will stay at the current number of partitions. However, if you’re doing a drastic coalesce, e.g. to num_partitions = 1, this may result in your computation taking place on fewer nodes than you like (e.g. one node in the case of num_partitions = 1). To avoid this, you can call repartition(). This will add a shuffle step, but means the current upstream partitions will be executed in parallel (per whatever the current partitioning is).

Parameters
num_partitionsint

The target number of partitions.

Returns
DataFrame

Examples

>>> kdf = ks.DataFrame({"age": [5, 5, 2, 2],
...         "name": ["Bob", "Bob", "Alice", "Alice"]}).set_index("age")
>>> kdf.sort_index()
name
age
2    Alice
2    Alice
5      Bob
5      Bob
>>> new_kdf = kdf.spark.coalesce(1)
>>> new_kdf.to_spark().rdd.getNumPartitions()
1
>>> new_kdf.sort_index()
name
age
2    Alice
2    Alice
5      Bob
5      Bob