1. A method for filtering keywords, the method comprising: receiving, by a processor, a first set of keywords; determining, by the processor, a first set of numbers associated with a first metric relating to the first set of keywords; determining, by the processor, a second set of numbers associated with a second metric relating to the first set of keywords; receiving, by the processor, at least one metric rule relating to the first and the second metric; determining, by the processor, a respective combination number for each keyword in the first set of keywords based on the first set of numbers, the second set of numbers, and the metric rule; and filtering, by the processor, the first set of keywords based on the respective combination numbers to produce a second set of keywords.