Function filter_keyvals 

pub fn filter_keyvals(
    events: Vec<Event>,
    key: &str,
    vals: &[Value],
) -> Vec<Event>

Drops events not matching the specified key and value(s)

Example

 key: a
 vals: [1,2]
 input:  [a:1][a:2][a:3][b:4]
 output: [a:1][a:2]