@quinck/collections
v0.4.2
Published
Allows extra operations on JavaScript collections: Array, Map and Set.
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collections
Allows extra operations on JavaScript collections: Array, Map and Set.
Overview
The operations are inspired from the Scala collection framework and aims to provide a simple way to perform operations like collect using match cases. Moreover add operations that allows to write fluent code.
Installation
npm i @quinck/collections
Tests
npm run test
Features
In this section will be presented some of the implemented operations.
| Collection | Operation | Description |
| -------- | -------- | -------- |
| Array
| groupBy
| Perform a group by operation, allowing to create a Map
from an Array
. The user has only to specify a function to obtain a the key from an element of the Array
. It also allow to transform each element in a new element letting the user specifying a function to evaluate the new values. The resulting map will contain the different keys generated |
| Array
| groupByToDictionary
| Similar to the groupBy
, but instead of a Map this will create an object. The created object will have as keys all the different keys generated. |
| Array
| simpleGroupBy
| Simplified version of the groupBy
, this operation will not allow to specify a mapper function for the values. In this case for each key will be generated and Array
of values referring to that key. |
| Array
| simpleGroupByToDictionary
| Simplified version of the groupByToDictionary
, this operation will not allow to specify a mapper function for the values. In this case for each key will be generated and Array
of values referring to that key. |
| Array
| singleCollect
| It performs Array.filter
and Array.map
operations in a single operation (browsing the elements of the array once). It allow to specify a filter and a mapper function. The elements that match the filter will be kept and the others will be discarded. Moreover as in Scala also here is possible to specify the default case that will take care of the elements that didn't matched the filter. |
| Array
| collect
| This operation tries to perform the collect
operation of the Scala collection framework. As in Scala is possible to use the match
construct, infact the collect
allows to specify an ordered Array
of MatchCase
. Starting from the first to the last MatchCase
, if an element of the Array
satisfy the filter the relative mapper will be applied. As in Scala only the first successful case will be cosidered. Moreover as in the collect
is possible to specify the default case specifying teh relative mapper. |
| Array
| chunckify
| Considering n
the the length of the array and size
the number of items per chunck. Splits array items in sn=n/size
, rounded up, arrays. The first sn-1
resulting arrays are of length equals to size
, while the last array cloud have a length between 1
and size
inclusive. |
| Array
| toSet
| Transform an Array
into a Set
with unique values.|
| Array
| awaitAll
| Awaits all the promises elements of the Array
to be fulfilled. |
| Array
| tryToAwaitAll
| Awaits all the promises elements of the Array
to be settled. If a Promise
fulfills the item will be replaced with its awaited version, if a Promise
rejects the item will be replaced with the error reported. |
| Array
| awaitAllFulfilled
| Awaits all the promises elements of the Array
to be settled, discarding elements that does not fulfills. |
| Array
| awaitAllRejected
| Awaits all the promises elements of the Array
to be settled, taking only the rejected. |
| Map
| toArray
| Map
objects in JavaScript (or Typescript) are not really 'array-friendly'. In fact in order to obtain an Array
having a Map
you have to get all the entries, using map.entries()
, and then creating an Array
(i.e. using Array.from
). This way does not allow to have a fluent code, so in order to achieve this the additional method Map.toArray
transform a Map
in an Array
where each element is a pair of a key and the relative value. Doing this way is possible to have a fluent code.|
| Map
| keysArray
| Allow to get the keys of a Map
in an Array
in a fluent way.|
| Map
| valuesArray
| Allow to get the values of a Map
in an Array
in a fluent way.|
Usage
In this section will be showed some examples.
Array
GroupBy
const students = [
{
studentClass = "A",
studentGrade = 9,
studentName = "Earvin"
},
{
studentClass = "A",
studentGrade = 10,
studentName = "Michael"
},
{
studentClass = "B",
studentGrade = 9,
studentName = "James"
},
{
studentClass = "B",
studentGrade = 10,
studentName = "Kobe"
},
{
studentClass = "B",
studentGrade = 9,
studentName = "Stephen"
}
]
/* Lets find the best student per each class */
const bestStudents = students.groupBy(
/* group by student class */
({studentClass}) => studentClass,
student => student,
/*
* merge elements of the same group,
* in this case take the higher studentGrade
*/
(a,b) => a.studentGrade > b.studentGrade ? a : b
)
/*
bestStudents will contain:
A => {
studentClass = "A",
studentGrade = 10,
studentName = "Michael"
}
B => {
studentClass = "B",
studentGrade = 10,
studentName = "Kobe"
}
*/
Collect
const students = [
{
studentClass = "A",
studentGrade = 9,
studentName = "Earvin"
},
{
studentClass = "A",
studentGrade = 10,
studentName = "Michael"
},
{
studentClass = "B",
studentGrade = 9,
studentName = "James"
},
{
studentClass = "B",
studentGrade = 10,
studentName = "Kobe"
},
{
studentClass = "B",
studentGrade = 9,
studentName = "Stephen"
},
{
studentClass = "B",
studentGrade = 5,
studentName = "Kevin"
}
]
/* Lets the students names of the class A */
const classAStudentsNames = students.singleCollect(
({studentClass}) => studentClass === "A",
({studentName}) => studentName
)
/*
classAStudentsNames will be:
["Earvin","Michael"]
*/
/* Lets perform this operations:
give a scholarship to students with grade equals to 10
pass students with a grade greater than or equals to 6
fail other students
*/
const studentsWithStatus = students.collect([
[
({studentGrade}) => studentGrade === 10,
student => ({...student, status: "scholarship"})
],
[
({studentGrade}) => studentGrade >= 6,
student => ({...student, status: "pass"})
]
], student => ({...student, status: "fail"})
)
/*
studentsWithStatus will be:
[
{
studentClass = "A",
studentGrade = 9,
studentName = "Earvin",
status: "pass"
},
{
studentClass = "A",
studentGrade = 10,
studentName = "Michael",
status: "scholarship"
},
...
{
studentClass = "B",
studentGrade = 5,
studentName = "Kevin",
status: "fail"
}
]
*/
Map
toArray
const map = new Map([1,10],[2,20],[3,30])
const result = map.toArray() /* [[1,10],[2,20],[3,30]] */
.filter(([key]) => key > 2) /* [[3,30]] */
Mixing
const map = new Map([1,10],[2,20],[3,30])
const result = map.toArray() /* [[1,10],[2,20],[3,30]] */
.singleCollect(
([key]) => key > 2,
([,value]) => [value],
(a,b) => a.concat(b)
)
/*
result = [30]
*/
Contact
- Quinck: [email protected]
- Stefano Righini: [email protected]