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# PySpark RDD | countByKey method

schedule Aug 12, 2023
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PySpark RDD's `countByKey(~)` method groups by the key of the elements in a pair RDD, and counts each group.

# Parameters

This method does not take in any parameter.

# Return Value

A `DefaultDict[key,int]`.

# Examples

Consider the following PySpark pair RDD:

``` rdd = sc.parallelize([("a",5),("a",1),("b",2),("c",4)])rdd.collect() [('a', 5), ('a', 1), ('b', 2), ('c', 4)] ```

Here, we are using the `parallelize(~)` method to create a RDD.

## Getting the count of each group in PySpark Pair RDD

To group by the key, and get the count of each group:

``` rdd.countByKey() defaultdict(int, {'a': 2, 'b': 1, 'c': 1}) ```

Here, the returned value is `DefaultDict`, which is basically a dictionary in which accessing values that do not exist in the dictionary will return a `0` instead of throwing an error.

You can access the count of a key just as you would for an ordinary dictionary:

``` counts = rdd.countByKey()counts["a"] 2 ```

Accesing counts of keys that do not exist will return `0`:

``` counts = rdd.countByKey()counts["z"] 0 ```
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