FilterMap Operator

The Filter-Map Operator is a tool that combines both a filter and a map at the same time. The operator here will be used to detect whether or not a sentence is a simple math addition equation with the filter and if so, it will be mapped to a string with the answer.

Prerequisites

This guide uses local Fluvio cluster. If you need to install it, please follow the instructions at here.

Transformation

Below is an example of a transform function using filter-map. The function first tries match the string to a regex under the form of a+b= where a and b are integers. Because regex is not in rust's standard library we have to import the library. Thus, the example below contains an example for dependencies with regex imported.

    transforms:
      - operator: filter-map 
        dependencies:
          - name: regex
            version: "1"
        run: |
          fn get_sentence_length(input: String) -> Result<Option<String> > {
            let re = regex::Regex::new(r"^(\d+)\+(\d+)=$").unwrap();
            if let Some(num) = re.captures(&input) {
                let a: i32 = num.get(1).unwrap().as_str().parse().unwrap();
                let b: i32 = num.get(2).unwrap().as_str().parse().unwrap();
                return Ok(Some(format!("{}{}",input,(a+b))));
            } else{
                return Ok(None);
            }
          }

A filter map returns an Option that could either be None or a Some. In this case, if the string does not match up to the regex it returns a None. If it does, it returns the computed value.

Running the Example

Copy and paste following config and save it as dataflow.yaml.

# dataflow.yaml
apiVersion: 0.5.0
meta:
  name: filter-map-example
  version: 0.1.0
  namespace: examples

config:
  converter: raw

topics:
  sentences:
    schema:
      value:
        type: string
  domath:
    schema:
      value:
        type: string

services:
  filter-map-service:
    sources:
      - type: topic
        id: sentences

    transforms:
      - operator: filter-map 
        dependencies:
          - name: regex
            version: "1"
        run: |
          fn do_addition(input: String) -> Result<Option<String> > {
            let re = regex::Regex::new(r"^(\d+)\+(\d+)=$").unwrap();
            if let Some(num) = re.captures(&input) {
                let a: i32 = num.get(1).unwrap().as_str().parse().unwrap();
                let b: i32 = num.get(2).unwrap().as_str().parse().unwrap();
                return Ok(Some(format!("{}{}",input,(a+b))));
            } else{
                return Ok(None);
            }
          }

    sinks:
      - type: topic
        id: domath

To run example:

$ sdf run --ephemeral

Produce sentences to in sentence topic:

$ echo "hello+world=" | fluvio produce sentences
$ echo "9999+1=" | fluvio produce sentences

Consume topic domath to retrieve the result in another terminal:

$ fluvio consume domath -Bd
9999+1=10000

Only strings matching the required format gets computed.

Cleanup

Exit sdf terminal and clean-up. The --force flag removes the topics:

$ sdf clean --force

Conclusion

We just covered another basic operator in SDF, the Filter-Map Operator.