Counts the number of elements within each aggregation. The Count transform has three varieties:

• Count.globally() counts the number of elements in the entire PCollection. The result is a collection with a single element.
• Count.perKey() counts how many elements are associated with each key. It ignores the values. The resulting collection has one output for every key in the input collection.
• Count.perElement() counts how many times each element appears in the input collection. The output collection is a key-value pair, containing each unique element and the number of times it appeared in the original collection.

Examples

Example 1: Count.globally

Example 2: Count.perKey

• ApproximateUnique estimates the number of distinct elements or distinct values in key-value pairs
• Sum computes the sum of elements in a collection