Extract scalar values in Flux

To extract scalar values from output:

  1. or extract a row from the input stream.
  2. Use the returned array or record to reference scalar values.

The samples on this page use the .

Current limitations

  • The InfluxDB user interface (UI) does not currently support raw scalar output. Use to add scalar values to output data.

Flux formats query results as a stream of tables. Both findColumn() and extract the first table in a stream of tables whose group key values match the .

Extract the correct table

Use the to output an array of values from a specific column in the extracted table.

See Sample data below.

Use a variable to store the array of values. In the example below, SFOTemps represents the array of values. Reference a specific index (integer starting from 0) in the array to return the value at that index.

  1. SFOTemps = sampleData
  2.     |> findColumn(
  3.         fn: (key) => key._field == "temp" and key.location == "sfo",
  4.         column: "_value",
  5.     )
  7. SFOTemps
  9. SFOTemps[0]
  10. // Returns 65.1
  12. SFOTemps[2]
  13. // Returns 66.3

Use the to output data from a single row in the extracted table. Specify the index of the row to output using the parameter. The function outputs a record with key-value pairs for each column.

Use an extracted row record

Use a variable to store the extracted row record. In the example below, tempInfo represents the extracted row. Use to reference keys in the record.

  1. tempInfo = sampleData
  2.     |> findRecord(
  3.         fn: (key) => key._field == "temp" and key.location == "sfo",
  4.         idx: 0,
  5.     )
  7. tempInfo
  8. // Returns {
  9. //   _time:2019-11-11T12:00:00Z,
  10. //   _field:"temp",
  11. //   location:"sfo",
  12. //   _value: 65.1
  13. // }
  15. tempInfo._time
  16. // Returns 2019-11-11T12:00:00Z
  17. tempInfo.location

Create custom helper functions to extract scalar values from query output.

Extract a scalar field value
Extract scalar row data
  1. // Define a helper function to extract a row as a record
  2. getRow = (tables=<-, field, idx=0) => {
  3.     extract = tables
  4.         |> findRecord(fn: (key) => true, idx: idx)
  6.     return extract
  7. }
  9. // Use the helper function to define a variable
  10. lastReported = sampleData
  11.     |> last()
  12.     |> getRow(field: "temp")
  14. "The last location to report was ${lastReported.location}.
  15. The temperature was ${string(v: lastReported._value)}°F."
  17. // Returns:
  18. // The last location to report was kord.
  19. // The temperature was 38.9°F.

Place the following at the beginning of your query to use the sample data: