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Lambda functions for Bicep

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This article describes the lambda functions to use in Bicep. Lambda expressions (or lambda functions) are essentially blocks of code that can be passed as an argument. They can take multiple parameters, but are restricted to a single line of code. In Bicep, lambda expression is in this format:

<lambda variable> => <expression>

Note

The lambda functions are only supported in Bicep CLI version 0.10.X or higher.

Limitations

Bicep lambda function has these limitations:

  • Lambda expression can only be specified directly as function arguments in these functions: filter(), map(), reduce(), sort(), and toObject().
  • Using lambda variables (the temporary variables used in the lambda expressions) inside resource or module array access isn't currently supported.
  • Using lambda variables inside the listKeys function isn't currently supported.
  • Using lambda variables inside the reference function isn't currently supported.

filter

filter(inputArray, lambda expression)

Filters an array with a custom filtering function.

Namespace: sys.

Parameters

Parameter Required Type Description
inputArray Yes array The array to filter.
lambda expression Yes expression The lambda expression is applied to each input array element. If the result is true, the item will be included in the output array; otherwise, the item is discarded.

Return value

An array.

Examples

The following examples show how to use the filter function.

var dogs = [
  {
    name: 'Evie'
    age: 5
    interests: ['Ball', 'Frisbee']
  }
  {
    name: 'Casper'
    age: 3
    interests: ['Other dogs']
  }
  {
    name: 'Indy'
    age: 2
    interests: ['Butter']
  }
  {
    name: 'Kira'
    age: 8
    interests: ['Rubs']
  }
]

output oldDogs array = filter(dogs, dog => dog.age >=5)

The output from the preceding example shows the dogs that are five or older:

Name Type Value
oldDogs Array [{"name":"Evie","age":5,"interests":["Ball","Frisbee"]},{"name":"Kira","age":8,"interests":["Rubs"]}] 
var itemForLoop = [for item in range(0, 10): item]

output filteredLoop array = filter(itemForLoop, i => i > 5)
output isEven array = filter(range(0, 10), i => 0 == i % 2)

The output from the preceding example:

Name Type Value
filteredLoop Array [6, 7, 8, 9]
isEven Array [0, 2, 4, 6, 8]

filterdLoop shows the numbers in an array that are greater than 5; and isEven shows the even numbers in the array.

map

map(inputArray, lambda expression)

Applies a custom mapping function to each element of an array.

Namespace: sys.

Parameters

Parameter Required Type Description
inputArray Yes array The array to map.
lambda expression Yes expression The lambda expression applied to each input array element, in order to generate the output array.

Return value

An array.

Example

The following example shows how to use the map function.

var dogs = [
  {
    name: 'Evie'
    age: 5
    interests: ['Ball', 'Frisbee']
  }
  {
    name: 'Casper'
    age: 3
    interests: ['Other dogs']
  }
  {
    name: 'Indy'
    age: 2
    interests: ['Butter']
  }
  {
    name: 'Kira'
    age: 8
    interests: ['Rubs']
  }
]

output dogNames array = map(dogs, dog => dog.name)
output sayHi array = map(dogs, dog => 'Hello ${dog.name}!')
output mapObject array = map(range(0, length(dogs)), i => {
  i: i
  dog: dogs[i].name
  greeting: 'Ahoy, ${dogs[i].name}!'
})

The output from the preceding example is:

Name Type Value
dogNames Array ["Evie","Casper","Indy","Kira"]
sayHi Array ["Hello Evie!","Hello Casper!","Hello Indy!","Hello Kira!"]
mapObject Array [{"i":0,"dog":"Evie","greeting":"Ahoy, Evie!"},{"i":1,"dog":"Casper","greeting":"Ahoy, Casper!"},{"i":2,"dog":"Indy","greeting":"Ahoy, Indy!"},{"i":3,"dog":"Kira","greeting":"Ahoy, Kira!"}]

dogNames shows the dog names from the array of objects; sayHi concatenates "Hello" and each of the dog names; and mapObject creates another array of objects.

reduce

reduce(inputArray, initialValue, lambda expression)

Reduces an array with a custom reduce function.

Namespace: sys.

Parameters

Parameter Required Type Description
inputArray Yes array The array to reduce.
initialValue Yes any Initial value.
lambda expression Yes expression The lambda expression used to aggregate the current value and the next value.

Return value

Any.

Example

The following examples show how to use the reduce function.

var dogs = [
  {
    name: 'Evie'
    age: 5
    interests: ['Ball', 'Frisbee']
  }
  {
    name: 'Casper'
    age: 3
    interests: ['Other dogs']
  }
  {
    name: 'Indy'
    age: 2
    interests: ['Butter']
  }
  {
    name: 'Kira'
    age: 8
    interests: ['Rubs']
  }
]
var ages = map(dogs, dog => dog.age)
output totalAge int = reduce(ages, 0, (cur, next) => cur + next)
output totalAgeAdd1 int = reduce(ages, 1, (cur, next) => cur + next)

The output from the preceding example is:

Name Type Value
totalAge int 18
totalAgeAdd1 int 19

totalAge sums the ages of the dogs; totalAgeAdd1 has an initial value of 1, and adds all the dog ages to the initial values.

output reduceObjectUnion object = reduce([
  { foo: 123 }
  { bar: 456 }
  { baz: 789 }
], {}, (cur, next) => union(cur, next))

The output from the preceding example is:

Name Type Value
reduceObjectUnion object {"foo":123,"bar":456,"baz":789}

The union function returns a single object with all elements from the parameters. The function call unionizes the key value pairs of the objects into a new object.

sort

sort(inputArray, lambda expression)

Sorts an array with a custom sort function.

Namespace: sys.

Parameters

Parameter Required Type Description
inputArray Yes array The array to sort.
lambda expression Yes expression The lambda expression used to compare two array elements for ordering. If true, the second element will be ordered after the first in the output array.

Return value

An array.

Example

The following example shows how to use the sort function.

var dogs = [
  {
    name: 'Evie'
    age: 5
    interests: ['Ball', 'Frisbee']
  }
  {
    name: 'Casper'
    age: 3
    interests: ['Other dogs']
  }
  {
    name: 'Indy'
    age: 2
    interests: ['Butter']
  }
  {
    name: 'Kira'
    age: 8
    interests: ['Rubs']
  }
]

output dogsByAge array = sort(dogs, (a, b) => a.age < b.age)

The output from the preceding example sorts the dog objects from the youngest to the oldest:

Name Type Value
dogsByAge Array [{"name":"Indy","age":2,"interests":["Butter"]},{"name":"Casper","age":3,"interests":["Other dogs"]},{"name":"Evie","age":5,"interests":["Ball","Frisbee"]},{"name":"Kira","age":8,"interests":["Rubs"]}]

toObject

toObject(inputArray, lambda expression, [lambda expression])

Converts an array to an object with a custom key function and optional custom value function. See items about converting an object to an array.

Namespace: sys.

Parameters

Parameter Required Type Description
inputArray Yes array The array used for creating an object.
lambda expression Yes expression The lambda expression used to provide the key predicate.
lambda expression No expression The lambda expression used to provide the value predicate.

Return value

An object.

Example

The following example shows how to use the toObject function with the two required parameters:

var dogs = [
  {
    name: 'Evie'
    age: 5
    interests: [ 'Ball', 'Frisbee' ]
  }
  {
    name: 'Casper'
    age: 3
    interests: [ 'Other dogs' ]
  }
  {
    name: 'Indy'
    age: 2
    interests: [ 'Butter' ]
  }
  {
    name: 'Kira'
    age: 8
    interests: [ 'Rubs' ]
  }
]

output dogsObject object = toObject(dogs, entry => entry.name)

The preceding example generates an object based on an array.

Name Type Value
dogsObject Object {"Evie":{"name":"Evie","age":5,"interests":["Ball","Frisbee"]},"Casper":{"name":"Casper","age":3,"interests":["Other dogs"]},"Indy":{"name":"Indy","age":2,"interests":["Butter"]},"Kira":{"name":"Kira","age":8,"interests":["Rubs"]}}

The following toObject function with the third parameter provides the same output.

output dogsObject object = toObject(dogs, entry => entry.name, entry => entry)

The following example shows how to use the toObject function with three parameters.

var dogs = [
  {
    name: 'Evie'
    properties: {
      age: 5
      interests: [ 'Ball', 'Frisbee' ]
    }
  }
  {
    name: 'Casper'
    properties: {
      age: 3
      interests: [ 'Other dogs' ]
    }
  }
  {
    name: 'Indy'
    properties: {
      age: 2
      interests: [ 'Butter' ]
    }
  }
  {
    name: 'Kira'
    properties: {
      age: 8
      interests: [ 'Rubs' ]
    }
  }
]
output dogsObject object = toObject(dogs, entry => entry.name, entry => entry.properties)

The preceding example generates an object based on an array.

Name Type Value
dogsObject Object {"Evie":{"age":5,"interests":["Ball","Frisbee"]},"Casper":{"age":3,"interests":["Other dogs"]},"Indy":{"age":2,"interests":["Butter"]},"Kira":{"age":8,"interests":["Rubs"]}}

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