Filter an Array

Exercise

Given the following input payload:

<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies,
      an evil sorceress, and her own childhood to become queen
      of the world.</description>
   </book>
   <book id="bk103">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse of a nanotechnology
      society in England, the young survivors lay the
      foundation for a new society.</description>
   </book>
   <book id="bk104">
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-03-10</publish_date>
      <description>In post-apocalypse England, the mysterious
      agent known only as Oberon helps to create a new life
      for the inhabitants of London. Sequel to Maeve
      Ascendant.</description>
   </book>
   <book id="bk105">
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-09-10</publish_date>
      <description>The two daughters of Maeve, half-sisters,
      battle one another for control of England. Sequel to
      Oberon's Legacy.</description>
   </book>
   <book id="bk106">
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-09-02</publish_date>
      <description>When Carla meets Paul at an ornithology
      conference, tempers fly as feathers get ruffled.</description>
   </book>
   <book id="bk107">
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>A deep sea diver finds true love twenty
      thousand leagues beneath the sea.</description>
   </book>
   <book id="bk108">
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <price>4.95</price>
      <publish_date>2000-12-06</publish_date>
      <description>An anthology of horror stories about roaches,
      centipedes, scorpions  and other insects.</description>
   </book>
   <book id="bk109">
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <price>6.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>After an inadvertant trip through a Heisenberg
      Uncertainty Device, James Salway discovers the problems
      of being quantum.</description>
   </book>
   <book id="bk110">
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-09</publish_date>
      <description>Microsoft's .NET initiative is explored in
      detail in this deep programmer's reference.</description>
   </book>
   <book id="bk111">
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-01</publish_date>
      <description>The Microsoft MSXML3 parser is covered in
      detail, with attention to XML DOM interfaces, XSLT processing,
      SAX and more.</description>
   </book>
   <book id="bk112">
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>49.95</price>
      <publish_date>2001-04-16</publish_date>
      <description>Microsoft Visual Studio 7 is explored in depth,
      looking at how Visual Basic, Visual C++, C#, and ASP+ are
      integrated into a comprehensive development
      environment.</description>
   </book>
</catalog>

Write a DataWeave transformation that produces the following output:

[
  {
    "author": "Corets, Eva",
    "title": "Oberon's Legacy",
    "genre": "Fantasy",
    "price": "5.95",
    "publish_date": "2001-03-10",
    "description": "In post-apocalypse England, the mysterious \n      agent known only as Oberon helps to create a new life \n      for the inhabitants of London. Sequel to Maeve \n      Ascendant."
  },
  {
    "author": "Corets, Eva",
    "title": "The Sundered Grail",
    "genre": "Fantasy",
    "price": "5.95",
    "publish_date": "2001-09-10",
    "description": "The two daughters of Maeve, half-sisters, \n      battle one another for control of England. Sequel to \n      Oberon's Legacy."
  },
  {
    "author": "Galos, Mike",
    "title": "Visual Studio 7: A Comprehensive Guide",
    "genre": "Computer",
    "price": "49.95",
    "publish_date": "2001-04-16",
    "description": "Microsoft Visual Studio 7 is explored in depth,\n      looking at how Visual Basic, Visual C++, C#, and ASP+ are \n      integrated into a comprehensive development \n      environment."
  }
]

Write a function that filters the elements of the list, taking the publication date and the date to filter by as parameters. In this case, every returned element is later than 2001-01-01.

Hints

• You can use the filter(items: Array<T>, criteria: (item: T, index: Number) -> Boolean) -> Array<T> function to filter an Array of elements against a criteria (a function). If you look at the parameters this criteria takes, you’ll see it is similar to the map function, except that here the function has to return a Boolean.
• You can also solve it with the filter selector [?()], putting the filter function inside it and passing the parameters it needs.
• A lambda would work, but this exercise asks you to write that function that filters by date and returns a Boolean value.

---

🔒🔓Show solution

Using the filter selector

%dw 2.0
output application/json

fun filtrarFecha(fechaLibro: Date, fechaFiltro: Date): Boolean = fechaLibro >= fechaFiltro
---
payload.catalog.*book[?(filtrarFecha($.publish_date, |2001-01-01|))]

Using the Filter function

%dw 2.0
output application/json

fun filtrarFecha(fechaLibro: Date, fechaFiltro: Date): Boolean = fechaLibro >= fechaFiltro
---
payload.catalog.*book filter filtrarFecha($.publish_date, |2001-01-01|)

Notes:

1. Note that in both cases the lambda $ is used to reach the item.
2. As the hints mention, you can use either the filter function or the filter selector ?[()]; inside they are quite similar, since all you pass along is the function doing the actual filtering, which is filtrarFecha()