Reduce

The reduce system takes key:value pairs as input from the map operation. The input needs to meet certain conditions and the reduce produces a new set of key:value pairs. The reduce operation can be either min, max, count, sum or average. The output of the reduce operation consists in a summary of all the inputs that were processed.

For example, the following reduction counts the reactions by player:

{
  "id": "countByPlayerReaction",
  "where": {
    "key": ["players", "<playerId>", "reaction"],
    "name": "<reaction>"
  },
  "key": ["reaction", "<playerId>", "<reaction>"],
  "values": ["$count"],
  "period": 250
}

The reduction output would look like this:

[
  {"key": ["reaction", "playerA", "like"], "value": {"count": 8}},
  {"key": ["reaction", "playerA", "love"], "value": {"count": 3}},
  {"key": ["reaction", "playerA", "sad"], "value": {"count": 5}},
  {"key": ["reaction", "playerA", "mad"], "value": {"count": 1}},
  {"key": ["reaction", "playerB", "like"], "value": {"count": 22}},
  {"key": ["reaction", "playerB", "love"], "value": {"count": 10}},
  {"key": ["reaction", "playerB", "sad"], "value": {"count": 1}},
  {"key": ["reaction", "playerB", "mad"], "value": {"count": 4}}
]

Reduce schema

id

Some string uniquely referencing the reduction rule, for possible modification after its creation.

where

Conditions to be met in order to produce another key:value pair. See Where schema for details.

period

The period in milliseconds. Determines the frequency of the reduction. A 250 ms period would means that the game would received the reduce 4 times per seconds.

key

An array of strings representing the new key produced.

Each string can be either:

• Alphanumeric string: A plain literal value.
• <anyText>: A named value taken from the input key.

value

An array of operations used to merge the inputs and generate the outputs. Each operation listed will produce one output.

Possible operations are:

• $min: Returns the minimum value among all inputs.
• $max: Returns the maximum value among all inputs.
• $count: Returns the number of times the key was encountered.
• $sum: Returns the sum of all input values added together.