generating map from list of objects having a map using java lambda8

up vote
9
down vote

favorite

I've an object,

class Object2{

     String name;

     String id;

     Map<String, String> customData;

}



class Object1{

     List<Object2> obj1List;

}

I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

add a comment |

up vote
9
down vote

favorite

I've an object,

class Object2{

     String name;

     String id;

     Map<String, String> customData;

}



class Object1{

     List<Object2> obj1List;

}

I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

add a comment |

up vote
9
down vote

favorite

I've an object,

class Object2{

     String name;

     String id;

     Map<String, String> customData;

}



class Object1{

     List<Object2> obj1List;

}

I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

I've an object,

class Object2{

     String name;

     String id;

     Map<String, String> customData;

}



class Object1{

     List<Object2> obj1List;

}

I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.

java lambda java-8 java-stream

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

edited Dec 5 at 23:41

Aomine

36.5k72961

edited Dec 5 at 23:41

Aomine

36.5k72961

edited Dec 5 at 23:41

Aomine

36.5k72961

asked Dec 5 at 23:33

sar

492

asked Dec 5 at 23:33

sar

492

asked Dec 5 at 23:33

sar

492

add a comment |

3 Answers
3

active

oldest

votes

up vote
6
down vote

Here's a way with lambdas and Java 8:

Map<String, String> map = new LinkedHashMap<>();

object1List.forEach(o1 -> 

        o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

1

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

add a comment |

up vote
4
down vote

Alternatively, you can perform Stream.flatMap and then use Map.putAll as

List<Object1> object1s = new ArrayList<>(); // initialise as you would

Map<String, String> finalCustomData = new LinkedHashMap<>();

object1s.stream() // Stream<Object1>

        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>

        .map(Object2::getCustomData) // Stream<Map<String, String>>

        .forEach(finalCustomData::putAll);

answered Dec 6 at 4:42

nullpointer

38.7k1074147

add a comment |

up vote
3
down vote

Use flatMap and toMap as follows:

List<Object1> source = ...

Map<String, String> result = 

     source.stream()

           .flatMap(e -> e.getObj1List().stream()

                               .flatMap(a -> a.getCustomData().entrySet().stream()))

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

or if you're dealing with a single Object1 object:

Object1 myObj = ...

Map<String, String> result = 

      myObj.getObj1List()

           .stream()

           .flatMap(a -> a.getCustomData().entrySet().stream())

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
6
down vote

Here's a way with lambdas and Java 8:

Map<String, String> map = new LinkedHashMap<>();

object1List.forEach(o1 -> 

        o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

1

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

add a comment |

up vote
6
down vote

Here's a way with lambdas and Java 8:

Map<String, String> map = new LinkedHashMap<>();

object1List.forEach(o1 -> 

        o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

1

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

add a comment |

up vote
6
down vote

Here's a way with lambdas and Java 8:

Map<String, String> map = new LinkedHashMap<>();

object1List.forEach(o1 -> 

        o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

Here's a way with lambdas and Java 8:

Map<String, String> map = new LinkedHashMap<>();

object1List.forEach(o1 -> 

        o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

edited Dec 6 at 9:53

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

answered Dec 6 at 0:37

Federico Peralta Schaffner

21.8k43369

1

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

add a comment |

1

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

weird naming convention in the question, but I guess you meant getObject1List()
– nullpointer
Dec 6 at 4:33

add a comment |

up vote
4
down vote

Alternatively, you can perform Stream.flatMap and then use Map.putAll as

List<Object1> object1s = new ArrayList<>(); // initialise as you would

Map<String, String> finalCustomData = new LinkedHashMap<>();

object1s.stream() // Stream<Object1>

        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>

        .map(Object2::getCustomData) // Stream<Map<String, String>>

        .forEach(finalCustomData::putAll);

answered Dec 6 at 4:42

nullpointer

38.7k1074147

add a comment |

up vote
4
down vote

Alternatively, you can perform Stream.flatMap and then use Map.putAll as

List<Object1> object1s = new ArrayList<>(); // initialise as you would

Map<String, String> finalCustomData = new LinkedHashMap<>();

object1s.stream() // Stream<Object1>

        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>

        .map(Object2::getCustomData) // Stream<Map<String, String>>

        .forEach(finalCustomData::putAll);

answered Dec 6 at 4:42

nullpointer

38.7k1074147

add a comment |

up vote
4
down vote

Alternatively, you can perform Stream.flatMap and then use Map.putAll as

List<Object1> object1s = new ArrayList<>(); // initialise as you would

Map<String, String> finalCustomData = new LinkedHashMap<>();

object1s.stream() // Stream<Object1>

        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>

        .map(Object2::getCustomData) // Stream<Map<String, String>>

        .forEach(finalCustomData::putAll);

answered Dec 6 at 4:42

nullpointer

38.7k1074147

Alternatively, you can perform Stream.flatMap and then use Map.putAll as

List<Object1> object1s = new ArrayList<>(); // initialise as you would

Map<String, String> finalCustomData = new LinkedHashMap<>();

object1s.stream() // Stream<Object1>

        .flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>

        .map(Object2::getCustomData) // Stream<Map<String, String>>

        .forEach(finalCustomData::putAll);

answered Dec 6 at 4:42

nullpointer

38.7k1074147

answered Dec 6 at 4:42

nullpointer

38.7k1074147

answered Dec 6 at 4:42

nullpointer

38.7k1074147

answered Dec 6 at 4:42

nullpointer

38.7k1074147

add a comment |

up vote
3
down vote

Use flatMap and toMap as follows:

List<Object1> source = ...

Map<String, String> result = 

     source.stream()

           .flatMap(e -> e.getObj1List().stream()

                               .flatMap(a -> a.getCustomData().entrySet().stream()))

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

or if you're dealing with a single Object1 object:

Object1 myObj = ...

Map<String, String> result = 

      myObj.getObj1List()

           .stream()

           .flatMap(a -> a.getCustomData().entrySet().stream())

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

add a comment |

up vote
3
down vote

Use flatMap and toMap as follows:

List<Object1> source = ...

Map<String, String> result = 

     source.stream()

           .flatMap(e -> e.getObj1List().stream()

                               .flatMap(a -> a.getCustomData().entrySet().stream()))

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

or if you're dealing with a single Object1 object:

Object1 myObj = ...

Map<String, String> result = 

      myObj.getObj1List()

           .stream()

           .flatMap(a -> a.getCustomData().entrySet().stream())

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

add a comment |

up vote
3
down vote

Use flatMap and toMap as follows:

List<Object1> source = ...

Map<String, String> result = 

     source.stream()

           .flatMap(e -> e.getObj1List().stream()

                               .flatMap(a -> a.getCustomData().entrySet().stream()))

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

or if you're dealing with a single Object1 object:

Object1 myObj = ...

Map<String, String> result = 

      myObj.getObj1List()

           .stream()

           .flatMap(a -> a.getCustomData().entrySet().stream())

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

Use flatMap and toMap as follows:

List<Object1> source = ...

Map<String, String> result = 

     source.stream()

           .flatMap(e -> e.getObj1List().stream()

                               .flatMap(a -> a.getCustomData().entrySet().stream()))

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

or if you're dealing with a single Object1 object:

Object1 myObj = ...

Map<String, String> result = 

      myObj.getObj1List()

           .stream()

           .flatMap(a -> a.getCustomData().entrySet().stream())

           .collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

edited Dec 5 at 23:44

answered Dec 5 at 23:37

Aomine

36.5k72961

answered Dec 5 at 23:37

Aomine

36.5k72961

answered Dec 5 at 23:37

Aomine

36.5k72961

add a comment |

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