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Providing a JsonFormat for a Sequence of Objects


Providing a JsonFormat for a Sequence of Objects

By : Fayssal Fellah
Date : November 17 2020, 08:25 AM
This might help you Look at the source of spray.json.CollectionFormats.
Here is a runnable implementation:
code :
import spray.json._

class Adress(val streetname: String, val plz: BigDecimal, val city: String)

class Person(val name: String, val adresses: Seq[Adress])

object PersonJsonProtocol extends DefaultJsonProtocol {
  implicit object AdressJsonFormat extends RootJsonFormat[Adress] {
    def write(addr: Adress) = JsObject(Map(
      "streetname" -> JsString(addr.streetname),
      "plz" -> JsNumber(addr.plz),
      "city" -> JsString(addr.city)
    ))
    def read(value: JsValue): Adress = ???
  }
  implicit object PersonJsonFormat extends RootJsonFormat[Person] {
    def write(pers: Person) = JsObject(Map(
      "name" -> JsString(pers.name),
      "adresses" -> JsArray(pers.adresses.map(_.toJson).toList)
    ))
    def read(value: JsValue): Person = ???
  }
}

object Main extends App {
  import PersonJsonProtocol._
  val person = new Person("joe", Seq(new Adress("street", 123, "city")))
  println("poso's default toString: %s".format(person))
  val personJVal = person.toJson
  println("JValue's toString: %s".format(personJVal))
  val personJson = personJVal.prettyPrint
  println("pretty-printing: %s".format(personJson))
}
poso's default toString: Person@680ccad
JValue's toString: {"name":"joe","adresses":[{"streetname":"street","plz":123,"city":"city"}]}
pretty-printing: {
  "name": "joe",
  "adresses": [{
    "streetname": "street",
    "plz": 123,
    "city": "city"
  }]
}


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Compression of sequence of integers providing random access

Compression of sequence of integers providing random access


By : Walter
Date : March 29 2020, 07:55 AM
Hope this helps If all your integers have the same frequency, then a fair approximation to optimal compression will be ceil(log2(k)) bits per integer. You can access a bit-array of these in constant time.
If k is painfully small (like 3), the above method may waste a fair amount of space. But, you can combine a fixed number of your small integers into a base-k number, which can fit more efficiently into a fixed number of bits (you may also be able to fit the result conveniently into a standard-sized word). In any case, you can also access this coding in constant time.
code :
log2( n!/(f!)^k ) = log2(n!) - k * log2(f!)
~ n log2(n) - n log2(e) - k ( f log2(f) - f log2(e) )
= n log2(n) - n log2(e) - n log2(f) + n log2(e)
= n ( log2(n) - log2(f) )
= n log2(n/f)
= n log2(k)
Turn sequence of objects with collection into a flat sequence

Turn sequence of objects with collection into a flat sequence


By : diana alejandra Hinc
Date : March 29 2020, 07:55 AM
To fix the issue you can do You're looking for this overload of Observable.SelectMany. This takes a projection function that returns an IEnumerable.
code :
public IObservable<B> C
{
    get { return _sequence.SelectMany(o => o.Collection); }
} 
Random Name Generator providing same name to multiple objects

Random Name Generator providing same name to multiple objects


By : Erik
Date : March 29 2020, 07:55 AM
wish helps you I'll supose placing the NameGenerator nameGen = new NameGenerator(); statement in the day function of World outsite the for loop will solve you're problem.
code :
NameGenerator nameGen = new NameGenerator();
for (int i = 0; i < 100; i++)
{
   Human h = new Human(nameGen.generateName(4, 8), nameGen.generateName(4, 12));
   worldHumans.Add(h);
   newWorldHumans.Add(h);
}
Providing a Sequence as a parameter to a method accepting varargs

Providing a Sequence as a parameter to a method accepting varargs


By : Parillah Latea
Date : March 29 2020, 07:55 AM
This might help you In the Spark DataFrame we have a select method that has a varargs second parameter: , You should wrap String to column:
code :
 Df.select(cols.map(x => col(x)) :_*)
Deserializing a json which contains @JsonFormat(shape=JsonFormat.Shape.ARRAY) and custom object using jackson

Deserializing a json which contains @JsonFormat(shape=JsonFormat.Shape.ARRAY) and custom object using jackson


By : Nisha
Date : March 29 2020, 07:55 AM
it fixes the issue JsonFormat does the trick but you also need to declare constructor with JsonCreator annotation. Take a look on below example:
code :
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.List;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        Response myPojo = mapper.readValue(jsonFile, Response.class);
        System.out.println(myPojo);
    }
}

class Response {

    private List<Value> values;

    public List<Value> getValues() {
        return values;
    }

    public void setValues(List<Value> values) {
        this.values = values;
    }

    @Override
    public String toString() {
        return "Response{" +
                "values=" + values +
                '}';
    }
}

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
class Value {

    private long timestamp;
    private float val;

    @JsonCreator
    public Value(@JsonProperty("timestamp") long timestamp, @JsonProperty("val") float val) {
        this.timestamp = timestamp;
        this.val = val;
    }

    public long getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(long timestamp) {
        this.timestamp = timestamp;
    }

    public float getVal() {
        return val;
    }

    public void setVal(float val) {
        this.val = val;
    }

    @Override
    public String toString() {
        return "Value{" +
                "timestamp=" + timestamp +
                ", val=" + val +
                '}';
    }
}
{
  "values": [
    [
      1552215648,
      18
    ],
    [
      123,
      12.24
    ]
  ]
}
Response{values=[Value{timestamp=1552215648, val=18.0}, Value{timestamp=123, val=12.24}]}
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