✎ DataWeave

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====== DataWeave ======

<code dw>
%dw 2.0
input payload json
output application/java
---
payload
</code>

<code dataweave>
%dw 2.0
output application/dw
---
payload
</code>

===== Working with Arrays / dw::core::Arrays =====

* **countBy**	Counts the elements in an array that return true when the matching function is applied to the value of each element.
  * **divideBy**	Breaks up an array into sub-arrays that contain the specified number of elements.
  * **drop**	Drops the first n elements. It returns the original array when n <= 0 and an empty array when n > sizeOf(array).
  * **dropWhile**	Drops elements from the array while the condition is met but stops the selection process when it reaches an element that fails to satisfy the condition.
  * **every**	Returns true if every element in the array matches the condition.
  * **firstWith**	Returns the first element that satisfies the condition, or returns null if no element meets the condition.
  * **indexOf**	Returns the index of the first occurrence of an element within the array. If the value is not found, the function returns -1.
  * **indexWhere**	Returns the index of the first occurrence of an element that matches a condition within the array. If no element matches the condition, the function returns -1.
  * **join**	Joins two arrays of objects by a given ID criteria.
  * **leftJoin**	Joins two arrays of objects by a given ID criteria.
  * **outerJoin**	Joins two array of objects by a given ID criteria.
  * **partition**	Separates the array into the elements that satisfy the condition from those that do not.
  * **slice**	Selects the interval of elements that satisfy the condition: from <= indexOf(array) < until
  * **some**	Returns true if at least one element in the array matches the specified condition.
  * **splitAt**	Splits an array into two at a given position.
  * **splitWhere**	Splits an array into two at the first position where the condition is met.
  * **sumBy**	Returns the sum of the values of the elements in an array.
  * **take**	Selects the first n elements. It returns an empty array when n <= 0 and the original array when n > sizeOf(array).
  * **takeWhile**	Selects elements from the array while the condition is met but stops the selection process when it reaches an element that fails to satisfy the condition.

===== dw::Core =====

====== reduce ======

Функция уменьшения используется для выполнения любых вычислений во время итерации массива, поэтому результат вычислений не теряется во время итерации. Для каждого элемента входного массива по порядку сокращение применяет лямбда-выражение (функцию) сокращения, а затем заменяет аккумулятор новым результатом. Лямбда-выражение может использовать как текущий элемент входного массива, так и текущее значение аккумулятора.

<code>
%dw 2.0
output json
---
payload reduce (n, total) -> total + n
</code>

<code>
%dw 2.0
output application/json
---
[2, 3] reduce ($ + $$)

Here

[2,3] – is the input array
    acc -> $$ will take the 1st item value = 2 (as acc is not initialized)
    $ will take the 2nd item value = 3 (as acc is not initialized)
    Loop count = no of item in array minus 1 (as acc is not initialized) = 2 – 1 = 1
        Acc = ($=3 + $$=2) = 5

So result will be 5
</code>

<code>
%dw 2.0
output application/json
---
[2,3] reduce ((item, acc = 4) -> acc + item)

Here

[2,3] – is the input array
    acc will take the initialized value = 4
    item will take 1st item value = 2 (as acc is initialized)
    Loop count = no of item in array (as acc is initialized) = 2
        Acc = acc + item -> 4 + 2 -> 6
        Acc = acc + item -> 6 + 3 -> 9

So result will be 9
</code>

===== Working with Objects / dw::core::Objects =====

* **divideBy**	Breaks up an object into sub-objects that contain the specified number of key-value pairs.
  * **entrySet**	Returns an array of key-value pairs that describe the key, value, and any attributes in the input object.
  * **everyEntry**	Returns true if every entry in the object matches the condition.
  * **keySet**	Returns an array of key names from an object.
  * **mergeWith**	Appends any key-value pairs from a source object to a target object.
  * **nameSet**	Returns an array of keys from an object.
  * **someEntry**	Returns true if at least one entry in the object matches the specified condition.
  * **takeWhile**	Selects key-value pairs from the object while the condition is met.
  * **valueSet**	Returns an array of the values from key-value pairs in an object.

====== Ссылки ======

* https://docs.mulesoft.com/dataweave/latest/

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