Difference between Coalesce and Repartition

The coalesce reduces the number of partitions in a DataFrame. 

The repartition either increase or decrease the number of partitions in a DataFrame.

The repartition algorithm does a full shuffle of the data and creates equal sized partitions of data. coalesce combines existing partitions to avoid a full shuffle.

Summary Of Difference

coalesce()	repartition()
reduce the number of partitions	increase or decrease the number of partitions.
Tries to minimize data movement by avoiding network shuffle.	A network shuffle will be triggered which can increase data movement.
Creates unequal sized partitions	Creates equal sized partitions