Conditional

Creates an array with values specified by a series of where statements.

The obs function was designed to work with the variable assignment filter to simplify the assignment of more complicated variables. However, the obs function can be used with any filter which takes an obs function as an argument. Any functionality in the Where statements can be used with this obs function. The where operator parameter can be used to specify the logical operator used to combine conditions used in the where statement. The possible values are and (the default) and or. Note that it is possible to use the where operator option without the where statement. The option has no impact in that case.

This is a templated function which can be used to produce different types of output arrays:

• ObsFunction/Conditional produces floats

• IntObsFunction/Conditional produces ints

• StringObsFunction/Conditional produces strings

• DateTimeObsFunction/Conditional produces datetimes.

Input parameters:

cases (required; can take as many case statements as required)

A list of one or more individual cases. Each case contains a “where” statement and a “value” to assign should the where clause evaluate to true. Like all where clauses in ufo this can have multiple arguments, see the examples below.

defaultvalue (optional)

A default value to assign to the output array at the beginning of the processing. This is optional and if the value is not present the array will be initialised with missing data.

firstmatchingcase (optional with default value = true)

A boolean to determine whether the first or last matching case should be the value assigned. If true then the first matching case is assigned which is analogous to the python case logic and is the default behaviour. If this is false the value can be changed multiple times as each case is processed leading to the final matching case being the assigned value.

Example configuration:

function:
  name: ObsFunction/Conditional
  options:
    defaultvalue: 9.0
    firstmatchingcase: true
    cases:
    - where:
      - variable:
          name: MetaData/float_variable_1
        minvalue: 4
      - variable:
          name: MetaData/float_variable_2
        minvalue: -11.75
      value: 75.5
    - where:
      - variable:
          name: MetaData/int_variable_1
        is_in: 1
      value: 3.0

In the above example, the return value of the obs function is initialised to 9.0. The first case tests where MetaData/float_variable_1 has a minimum value of 4.0 and also where MetaData/float_variable_2 has a minimum value of -11.75, assigning a return value of 75.5 if these where clauses both evaluate to true. Since firstmatchingcase is set to true, these values are not overwritten by subsequent cases. The second case tests where MetaData/int_variable_1 is equal to 1 and if so assigns a return value of 3.0.

For further examples see the unit test yaml in ufo which can be found here.