Logstash filter add new calculated float value

[azeiner (Andreas Zeiner)]

I've got Data from a Json Object and what i want is to calculate some Values of the same Object
e.g.

   filter {
      json {
        source => "message"
		
      }

	  mutate {
		add_field => { 
		"xxx1" => "Float(%{[BME680][Temperature]}*1.634*%{[BME680][Pressure]})"
                "xxx2" => "Float(%{[BME680][Temperature1]}*1.634*%{[BME680][Pressure1]})"
                "xxx3" => "Float(%{[xxx1]}-%{[xxx2]})"
						}
	  }
    }

The calculation is hier just for demo purposes - it's just multipling some fields and devide them.

The action should be that:
xxx1 should be calculated from some fields
xxx2 should be calculated from some fields
xxx3 should be calculated from both fields

ist this possible in logstash and how can it be done?

i only get the following

Aug 9, 2022 @ 14:13:39.104 Float(31.91.63410*993.0)

so i get the value as a String not as a number!

[vilman]

I would use ruby:

 ruby {
            code => "event.set('[xxx1]' , event.get('[BME680][Temperature]').to_f * 1.634 * event.get('[BME680][Pressure]').to_f )"
          }

The '.to_f' in ruby converts those fields from string to float. Ideally that would be done earlier with mutate { convert => {"[BME680][Temperature]" => "float" }}.

[azeiner (Andreas Zeiner)]

@vilman

 ruby {
            code => "event.set('[xxx1]' , event.get('[BME680][Temperature]').to_f * 1.634 * event.get('[BME680][Pressure]').to_f )"
          }

Thank you, i'll give it a try and will report back soon!

[azeiner (Andreas Zeiner)]

Thank you very much, it works perfectly!