Could you please give me an example of how to use the $all operator for my two elemMatch objects?
val elemMatch1 = foo()
val elemMatch2 = bar()
How can I perform the query of $all( elemMatch1, elemMatch2) (all documents where elemMatch1 and elemMatch2)?
I'm not sure how much sense it makes to mix $all and $elemMatch but from the docs $all follows:
{ <field>: { $all: [ <value> , <value1> ... ] }
$elemMatch follows:
{ array: { $elemMatch: <document> } }
Unfortunately, the casbah DSL won't help there as $all requires a list and $elemMatch expects a string, so you have to manually have to build the document:
import com.mongodb.casbah.Imports._
val coll = MongoClient()("test")("testB")
coll += MongoDBObject("array" -> List(
MongoDBObject("value1" -> 1, "value2" -> 0),
MongoDBObject("value1" -> 1, "value2" -> 2)
))
val elemMatch = MongoDBObject("$elemMatch" -> MongoDBObject("value1" -> 1, "value2" -> 2))
val query = "array" $all List(elemMatch)
coll.find(query).count
Related
I have a type defined as follows:
type Employee = {
Id: Guid
Name: string
Phone: string
Email: Option<string>
}
and an instance of this type:
let emp = {
Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
Name = "A"
Phone = "B"
Email = Some "E"
}
I want to extract the field names and values from this record type using reflection like the following:
let getFieldValueMappingOfARecordType (data: 'T) : seq<string * obj> =
let fieldValueMapping =
data.GetType()
|> FSharpType.GetRecordFields
|> Seq.map (
fun propertyInfo ->
(propertyInfo.Name, data |> propertyInfo.GetValue)
)
fieldValueMapping
Then invoking the above function with the instance of employee type
let mapping = getFieldValueMappingOfARecordType emp
|> Seq.toList
gives us:
val mapping : (string * obj) list =
[("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
("Email", Some "E")]
So far it's working well with non-optional type. But in case of optional types, it's returning the value of the field as either Some value or None. What I would like to do is to get the value when the field has Some value or make it null when it's None.
Essentially like the follwing:
val mapping : (string * obj) list =
[("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
("Email", "E")]
Or if the employee instance is like the following:
let emp = {
Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
Name = "A"
Phone = "B"
Email = None
}
Then,
val mapping : (string * obj) list =
[("Id", bc07e94c-b376-45a2-928b-508b888802c9); ("Name", "A"); ("Phone", "B");
("Email", null)]
This is what I have so far (non-working code):
open System
open Microsoft.FSharp.Reflection
open System.Reflection
type Employee = {
Id: Guid
Name: string
Phone: string
Email: Option<string>
}
let emp = {
Id = Guid "bc07e94c-b376-45a2-928b-508b888802c9"
Name = "A"
Phone = "B"
Email = Some "E"
}
let getSomeOrNull (t: Type) (o: obj) =
let opt = typedefof<option<_>>.MakeGenericType [| t |]
match (o :?> opt) with
| Some s ->
s
| None ->
null
let getValues (data: 'T) =
let values =
data.GetType()
|> FSharpType.GetRecordFields
|> Array.map (
fun propertyInfo ->
let value =
data |> propertyInfo.GetValue
let isOption =
propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() = typedefof<Option<_>>
match isOption with
| true ->
(propertyInfo.Name, (getSomeOrNull propertyInfo.PropertyType value))
| false ->
(propertyInfo.Name, value)
)
values
getValues emp
|> printfn "%A"
I think the only way to do this is with reflection:
let getSomeOrNull (t: Type) (o: obj) =
if isNull o then null
else t.GetProperty("Value").GetValue(o)
I think this should do the trick:
let getSomeOrNull (o: obj) =
match o with
| :? Option<string> as o -> a |> Option.toObj > box
| _ -> null
I am new at Kotlin and trying to catch up the language.
I have a function that returns DayofWeek as a key and an Int as a value.
The issue that I am facing is that I need to take a list of object that has another list of object inside that has an Int value which I need to save and increment for every time I see the same value.
Here is my function -
class OrdersAnalyzer {
data class Order(val orderId: Int, val creationDate: LocalDateTime, val orderLines: List<OrderLine>)
data class OrderLine(val productId: Int, val name: String, val quantity: Int, val unitPrice: BigDecimal)
fun totalDailySales(orders: List<Order>) : Map<DayOfWeek, Int> {
val map: MutableMap<DayOfWeek, Int>? = mutableMapOf(
Pair(DayOfWeek.SUNDAY, 0),
Pair(DayOfWeek.MONDAY, 0),
Pair(DayOfWeek.TUESDAY, 0),
Pair(DayOfWeek.WEDNESDAY, 0),
Pair(DayOfWeek.THURSDAY, 0),
Pair(DayOfWeek.FRIDAY, 0),
Pair(DayOfWeek.SATURDAY, 0)
)
for (order in orders) {
val dayOfWeek = order.creationDate.dayOfWeek
var quantity = 0
map?.put(dayOfWeek, quantity)
}
return map!!
}
}
So the issues I am facing right now are 2 -
1) How can I increment the value of each pair when it is the corrent DayOfWeek? I don't want to replace, I want to add it to the last value.
2) When returning the Map, I do not want to return the DayOfWeeks that have the value of 0. How can I do that?
Here is a modified version of the elegant answer provided by Arjan, with some test code.
Updated the answer after the comment from Alon Shlider -- now counting all order item quantities grouped by day of the week:
fun totalDailySales(orders: List<Order>): Map<DayOfWeek, Int> =
orders.groupBy { it.creationDate.dayOfWeek }
.mapValues { sumItemQuantities(it.value) }
fun sumItemQuantities(orders: List<Order>) =
orders.flatMap { it.orderLines.map { line -> line.quantity } }.sum()
fun main() {
val orders = listOf(
Order(
1,
LocalDateTime.now().minusDays(2),
listOf(
OrderLine(6, "laptop", 28, 1200.toBigDecimal())
)
),
Order(
2,
LocalDateTime.now().minusDays(1),
listOf(
OrderLine(496, "VR headset", 6, 400.toBigDecimal())
)
)
)
println(totalDailySales(orders))
}
Output:
{FRIDAY=28, SATURDAY=6}
With this approach, Kotlin functions do the grouping and counting for you. The groupBy function creates a map from DayOfWeek to a list of orders (grouping all orders with the same day of week in a list). The mapValues function transforms that map by replacing the lists with the result of the sumItemQuantities function (for each list).
In the for loop in your code, you can retrieve the current quantity for a specific day (or use zero if it isn't set yet), increase it by the right amount and then store it. To return only the map entries with non zero values, you could filter (return totalsPerDay.filter { it.value > 0 }) or start with an empty map. This is your function with some changes:
fun totalDailySales(orders: List<Order>): Map<DayOfWeek, Int> {
val totalsPerDay = mutableMapOf<DayOfWeek, Int>()
for (order in orders) {
val dayOfWeek = order.creationDate.dayOfWeek
val currentQuantity = totalsPerDay[dayOfWeek] ?: 0
// This is not the best way to increment by the sum of the order
// item quantities...
val orderItemQuantities = sumItemQuantities(listOf(order))
totalsPerDay[dayOfWeek] = currentQuantity + orderItemQuantities
}
return totalsPerDay
}
Output after calling it:
println(OrdersAnalyzer().totalDailySales(orders))
{FRIDAY=28, SATURDAY=6}
Updated answer (also thanks to Freek de Bruijn), with some test code.
I think it would be something like this:
fun totalDailySales(orders: List<Order>) : Map<DayOfWeek, Int> =
orders.groupBy { it.creationDate.dayOfWeek }
.mapValues { it.value.flatMap { it.orderLines } }
.mapValues { it.value.map { it.quantity } }
.mapValues { it.value.sum() }
groupBy creates a Map where the values are of type List<Order>, so you need to call a few steps to convert these values to Int. First we use flatMap to convert List<Order> to List<OrderLine> (map would convert to List<List<OrderLine>>). Then we use map to get the quantities out of List<OrderLine>, and finally sum() to add up all those quantities.
val orders = listOf(
Order(
2,
LocalDateTime.now().minusDays(2),
listOf(
OrderLine(5, "monitor", 10, 200.toBigDecimal()),
OrderLine(4, "keyboard", 5, 50.toBigDecimal())
)
)
)
println(totalDailySales(orders))
This results in the output:
{FRIDAY=15}
So it looks like the filter function on a Swift (2.x) dictionary returns a tuple array. My question is there an elegant solution to turning it back into a dictionary? Thanks in advance.
let dictionary: [String: String] = [
"key1": "value1",
"key2": "value2",
"key3": "value3"
]
let newTupleArray: [(String, String)] = dictionary.filter { (tuple: (key: String, value: String)) -> Bool in
return tuple.key != "key2"
}
let newDictionary: [String: String] = Dictionary(dictionaryLiteral: newTupleArray) // Error: cannot convert value of type '[(String, String)]' to expected argument type '[(_, _)]'
If you are looking for a more functional approach:
let result = dictionary.filter {
$0.0 != "key2"
}
.reduce([String: String]()) { (var aggregate, elem) in
aggregate[elem.0] = elem.1
return aggregate
}
reduce here is used to construct a new dictionary from the filtered tuples.
Edit: since var parameters has been deprecated in Swift 2.2, you need to create a local mutable copy of aggregate:
let result = dictionary.filter {
$0.0 != "key2"
}
.reduce([String: String]()) { aggregate, elem in
var newAggregate = aggregate
newAggregate[elem.0] = elem.1
return newAggregate
}
You can extend Dictionary so that it takes a sequence of tuples as initial values:
extension Dictionary {
public init<S: SequenceType where S.Generator.Element == (Key, Value)>(_ seq: S) {
self.init()
for (k, v) in seq { self[k] = v }
}
}
and then do
let newDictionary = Dictionary(newTupleArray)
For example I have a list of strings like:
val list = listOf("a", "b", "c", "d")
and I want to convert it to a map, where the strings are the keys.
I know I should use the .toMap() function, but I don't know how, and I haven't seen any examples of it.
You have two choices:
The first and most performant is to use associateBy function that takes two lambdas for generating the key and value, and inlines the creation of the map:
val map = friends.associateBy({it.facebookId}, {it.points})
The second, less performant, is to use the standard map function to create a list of Pair which can be used by toMap to generate the final map:
val map = friends.map { it.facebookId to it.points }.toMap()
From List to Map with associate function
With Kotlin 1.3, List has a function called associate. associate has the following declaration:
fun <T, K, V> Iterable<T>.associate(transform: (T) -> Pair<K, V>): Map<K, V>
Returns a Map containing key-value pairs provided by transform function applied to elements of the given collection.
Usage:
class Person(val name: String, val id: Int)
fun main() {
val friends = listOf(Person("Sue Helen", 1), Person("JR", 2), Person("Pamela", 3))
val map = friends.associate({ Pair(it.id, it.name) })
//val map = friends.associate({ it.id to it.name }) // also works
println(map) // prints: {1=Sue Helen, 2=JR, 3=Pamela}
}
From List to Map with associateBy function
With Kotlin, List has a function called associateBy. associateBy has the following declaration:
fun <T, K, V> Iterable<T>.associateBy(keySelector: (T) -> K, valueTransform: (T) -> V): Map<K, V>
Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given collection.
Usage:
class Person(val name: String, val id: Int)
fun main() {
val friends = listOf(Person("Sue Helen", 1), Person("JR", 2), Person("Pamela", 3))
val map = friends.associateBy(keySelector = { person -> person.id }, valueTransform = { person -> person.name })
//val map = friends.associateBy({ it.id }, { it.name }) // also works
println(map) // prints: {1=Sue Helen, 2=JR, 3=Pamela}
}
If you have duplicates in your list that you don't want to lose, you can do this using groupBy.
Otherwise, like everyone else said, use associate/By/With (which in the case of duplicates, I believe, will only return the last value with that key).
An example grouping a list of people by age:
class Person(val name: String, val age: Int)
fun main() {
val people = listOf(Person("Sue Helen", 31), Person("JR", 25), Person("Pamela", 31))
val duplicatesKept = people.groupBy { it.age }
val duplicatesLost = people.associateBy({ it.age }, { it })
println(duplicatesKept)
println(duplicatesLost)
}
Results:
{31=[Person#41629346, Person#4eec7777], 25=[Person#3b07d329]}
{31=Person#4eec7777, 25=Person#3b07d329}
Convert a Iteratable Sequence Elements to a Map in kotlin ,
associate vs associateBy vs associateWith:
*Reference:Kotlin Documentation
1- associate (to set both Keys & Values): Build a map that can set key & value elements :
IterableSequenceElements.associate { newKey to newValue } //Output => Map {newKey : newValue ,...}
If any of two pairs would have the same key the last one gets added to the map.
The returned map preserves the entry iteration order of the original array.
2- associateBy (just set Keys by calculation): Build a map that we can set new Keys, analogous elements will be set for values
IterableSequenceElements.associateBy { newKey } //Result: => Map {newKey : 'Values will be set from analogous IterableSequenceElements' ,...}
3- associateWith (just set Values by calculation): Build a map that we can set new Values, analogous elements will be set for Keys
IterableSequenceElements.associateWith { newValue } //Result => Map { 'Keys will be set from analogous IterableSequenceElements' : newValue , ...}
Example from Kotlin tips :
You can use associate for this task:
val list = listOf("a", "b", "c", "d")
val m: Map<String, Int> = list.associate { it to it.length }
In this example, the strings from list become the keys and their corresponding lengths (as an example) become the values inside the map.
That have changed on the RC version.
I am using val map = list.groupByTo(destinationMap, {it.facebookId}, { it -> it.point })
I have an existing map in Groovy.
I want to create a new map that has the same keys but different values in it.
Eg.:
def scores = ["vanilla":10, "chocolate":9, "papaya": 0]
//transformed into
def preference = ["vanilla":"love", "chocolate":"love", "papaya": "hate"]
Any way of doing it through some sort of closure like:
def preference = scores.collect {//something}
You can use collectEntries
scores.collectEntries { k, v ->
[ k, 'new value' ]
}
An alternative to using a map for the ranges would be to use a switch
def grade = { score ->
switch( score ) {
case 10..9: return 'love'
case 8..6: return 'like'
case 5..2: return 'meh'
case 1..0: return 'hate'
default : return 'ERR'
}
}
scores.collectEntries { k, v -> [ k, grade( v ) ] }
Nice, functional style solution(including your ranges, and easy to modify):
def scores = [vanilla:10, chocolate:9, papaya: 0]
// Store somewhere
def map = [(10..9):"love", (8..6):"like", (5..2):"meh", (1..0):"hate"]
def preference = scores.collectEntries { key, score -> [key, map.find { score in it.key }.value] }
// Output: [vanilla:love, chocolate:love, papaya:hate]
def scores = ["vanilla":10, "chocolate":9, "papaya": 0]
def preference = scores.collectEntries {key, value -> ["$key":(value > 5 ? "like" : "hate")]}
Then the result would be
[vanilla:like, chocolate:like, papaya:hate]
EDIT: If you want a map, then you should use collectEntries like tim_yates said.