Constructing list from multi level map in Java 8
11
I have a multi-level map as follows:
Map<String, Map<String, Student> outerMap =
{"cls1" : {"xyz" : Student(rollNumber=1, name="test1")},
"cls2" : {"abc" : Student(rollNumber=2, name="test2")}}
Now I want to construct a list of string from the above map as follows:
["In class cls1 xyz with roll number 1",
"In class cls2 abc with roll number 2"]
I have written as follows, but this is not working, in this context I have gone through the post as well: Java 8 Streams - Nested Maps to List, but did not get much idea.
List<String> classes = outerMap.keySet();
List<String> studentList = classes.stream()
.map(cls ->
outerMap.get(cls).keySet().stream()
.map(student -> "In class "+ cls +
student + " with roll number " +
outerMap.get(cls).get(student).getRollNum() +"n"
).collect(Collectors.toList());
java list java-8 hashmap
asked Jan 17 at 4:58
JoyJoy
1,12172353
add a comment |
11
I have a multi-level map as follows:
Map<String, Map<String, Student> outerMap =
{"cls1" : {"xyz" : Student(rollNumber=1, name="test1")},
"cls2" : {"abc" : Student(rollNumber=2, name="test2")}}
Now I want to construct a list of string from the above map as follows:
["In class cls1 xyz with roll number 1",
"In class cls2 abc with roll number 2"]
I have written as follows, but this is not working, in this context I have gone through the post as well: Java 8 Streams - Nested Maps to List, but did not get much idea.
List<String> classes = outerMap.keySet();
List<String> studentList = classes.stream()
.map(cls ->
outerMap.get(cls).keySet().stream()
.map(student -> "In class "+ cls +
student + " with roll number " +
outerMap.get(cls).get(student).getRollNum() +"n"
).collect(Collectors.toList());
java list java-8 hashmap
asked Jan 17 at 4:58
JoyJoy
1,12172353
add a comment |
11
11
11
3
I have a multi-level map as follows:
Map<String, Map<String, Student> outerMap =
{"cls1" : {"xyz" : Student(rollNumber=1, name="test1")},
"cls2" : {"abc" : Student(rollNumber=2, name="test2")}}
Now I want to construct a list of string from the above map as follows:
["In class cls1 xyz with roll number 1",
"In class cls2 abc with roll number 2"]
I have written as follows, but this is not working, in this context I have gone through the post as well: Java 8 Streams - Nested Maps to List, but did not get much idea.
List<String> classes = outerMap.keySet();
List<String> studentList = classes.stream()
.map(cls ->
outerMap.get(cls).keySet().stream()
.map(student -> "In class "+ cls +
student + " with roll number " +
outerMap.get(cls).get(student).getRollNum() +"n"
).collect(Collectors.toList());
java list java-8 hashmap
asked Jan 17 at 4:58
JoyJoy
1,12172353
I have a multi-level map as follows:
Map<String, Map<String, Student> outerMap =
{"cls1" : {"xyz" : Student(rollNumber=1, name="test1")},
"cls2" : {"abc" : Student(rollNumber=2, name="test2")}}
Now I want to construct a list of string from the above map as follows:
["In class cls1 xyz with roll number 1",
"In class cls2 abc with roll number 2"]
I have written as follows, but this is not working, in this context I have gone through the post as well: Java 8 Streams - Nested Maps to List, but did not get much idea.
List<String> classes = outerMap.keySet();
List<String> studentList = classes.stream()
.map(cls ->
outerMap.get(cls).keySet().stream()
.map(student -> "In class "+ cls +
student + " with roll number " +
outerMap.get(cls).get(student).getRollNum() +"n"
).collect(Collectors.toList());
java list java-8 hashmap
java list java-8 hashmap
asked Jan 17 at 4:58
JoyJoy
1,12172353
asked Jan 17 at 4:58
JoyJoy
1,12172353
asked Jan 17 at 4:58
JoyJoy
1,12172353
asked Jan 17 at 4:58
JoyJoy
1,12172353
asked Jan 17 at 4:58
JoyJoy
1,12172353
1,12172353
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
11
You can simply use Map.forEach for this operation as:
List<String> messages = new ArrayList<>();
outerMap.forEach((cls, students) ->
students.forEach((name, student) ->
messages.add(convertToMessage(cls, name, student.getRollNumber()))));
where convertToMessage is a util as :
// this could be made cleaner using 'format'
String convertToMessage(String cls, String studentName, String rollNumber) {
return "In class" + cls + "--> " + studentName + " with roll number: " + rollNumber;
}
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
add a comment |
5
You may do it like so,
List<String> formattedOutput = outerMap
.entrySet().stream()
.flatMap(e -> e.getValue().entrySet().stream().map(se -> "In class " + e.getKey()
+ " " + se.getKey() + " with roll number " + se.getValue().getRollNumber()))
.collect(Collectors.toList());
You have to use the flatMap operator instead of map operator.
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
add a comment |
2
One method use Java 8 Stream and lambda function:
String format = "In class %s %s with roll number %d";
List<String> result = new ArrayList<>();
outerMap.entrySet().stream()
.forEach(v -> {
String className = v.getKey();
v.getValue().entrySet().stream()
.forEach(stringStudentEntry -> result.add(String.format(format,className,stringStudentEntry.getKey(),stringStudentEntry.getValue().getRollNumber())));
});
answered Jan 17 at 5:34
TongChenTongChen
31529
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
11
You can simply use Map.forEach for this operation as:
List<String> messages = new ArrayList<>();
outerMap.forEach((cls, students) ->
students.forEach((name, student) ->
messages.add(convertToMessage(cls, name, student.getRollNumber()))));
where convertToMessage is a util as :
// this could be made cleaner using 'format'
String convertToMessage(String cls, String studentName, String rollNumber) {
return "In class" + cls + "--> " + studentName + " with roll number: " + rollNumber;
}
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
add a comment |
11
You can simply use Map.forEach for this operation as:
List<String> messages = new ArrayList<>();
outerMap.forEach((cls, students) ->
students.forEach((name, student) ->
messages.add(convertToMessage(cls, name, student.getRollNumber()))));
where convertToMessage is a util as :
// this could be made cleaner using 'format'
String convertToMessage(String cls, String studentName, String rollNumber) {
return "In class" + cls + "--> " + studentName + " with roll number: " + rollNumber;
}
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
add a comment |
11
11
11
You can simply use Map.forEach for this operation as:
List<String> messages = new ArrayList<>();
outerMap.forEach((cls, students) ->
students.forEach((name, student) ->
messages.add(convertToMessage(cls, name, student.getRollNumber()))));
where convertToMessage is a util as :
// this could be made cleaner using 'format'
String convertToMessage(String cls, String studentName, String rollNumber) {
return "In class" + cls + "--> " + studentName + " with roll number: " + rollNumber;
}
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
You can simply use Map.forEach for this operation as:
List<String> messages = new ArrayList<>();
outerMap.forEach((cls, students) ->
students.forEach((name, student) ->
messages.add(convertToMessage(cls, name, student.getRollNumber()))));
where convertToMessage is a util as :
// this could be made cleaner using 'format'
String convertToMessage(String cls, String studentName, String rollNumber) {
return "In class" + cls + "--> " + studentName + " with roll number: " + rollNumber;
}
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
edited Jan 17 at 5:47
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
answered Jan 17 at 5:04
nullpointernullpointer
46.2k1198188
46.2k1198188
add a comment |
add a comment |
5
You may do it like so,
List<String> formattedOutput = outerMap
.entrySet().stream()
.flatMap(e -> e.getValue().entrySet().stream().map(se -> "In class " + e.getKey()
+ " " + se.getKey() + " with roll number " + se.getValue().getRollNumber()))
.collect(Collectors.toList());
You have to use the flatMap operator instead of map operator.
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
add a comment |
5
You may do it like so,
List<String> formattedOutput = outerMap
.entrySet().stream()
.flatMap(e -> e.getValue().entrySet().stream().map(se -> "In class " + e.getKey()
+ " " + se.getKey() + " with roll number " + se.getValue().getRollNumber()))
.collect(Collectors.toList());
You have to use the flatMap operator instead of map operator.
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
add a comment |
5
5
5
You may do it like so,
List<String> formattedOutput = outerMap
.entrySet().stream()
.flatMap(e -> e.getValue().entrySet().stream().map(se -> "In class " + e.getKey()
+ " " + se.getKey() + " with roll number " + se.getValue().getRollNumber()))
.collect(Collectors.toList());
You have to use the flatMap operator instead of map operator.
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
You may do it like so,
List<String> formattedOutput = outerMap
.entrySet().stream()
.flatMap(e -> e.getValue().entrySet().stream().map(se -> "In class " + e.getKey()
+ " " + se.getKey() + " with roll number " + se.getValue().getRollNumber()))
.collect(Collectors.toList());
You have to use the flatMap operator instead of map operator.
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
edited Jan 17 at 5:46
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
answered Jan 17 at 5:16
Ravindra RanwalaRavindra Ranwala
8,85531634
8,85531634
add a comment |
add a comment |
2
One method use Java 8 Stream and lambda function:
String format = "In class %s %s with roll number %d";
List<String> result = new ArrayList<>();
outerMap.entrySet().stream()
.forEach(v -> {
String className = v.getKey();
v.getValue().entrySet().stream()
.forEach(stringStudentEntry -> result.add(String.format(format,className,stringStudentEntry.getKey(),stringStudentEntry.getValue().getRollNumber())));
});
answered Jan 17 at 5:34
TongChenTongChen
31529
add a comment |
2
One method use Java 8 Stream and lambda function:
String format = "In class %s %s with roll number %d";
List<String> result = new ArrayList<>();
outerMap.entrySet().stream()
.forEach(v -> {
String className = v.getKey();
v.getValue().entrySet().stream()
.forEach(stringStudentEntry -> result.add(String.format(format,className,stringStudentEntry.getKey(),stringStudentEntry.getValue().getRollNumber())));
});
answered Jan 17 at 5:34
TongChenTongChen
31529
add a comment |
2
2
2
One method use Java 8 Stream and lambda function:
String format = "In class %s %s with roll number %d";
List<String> result = new ArrayList<>();
outerMap.entrySet().stream()
.forEach(v -> {
String className = v.getKey();
v.getValue().entrySet().stream()
.forEach(stringStudentEntry -> result.add(String.format(format,className,stringStudentEntry.getKey(),stringStudentEntry.getValue().getRollNumber())));
});
answered Jan 17 at 5:34
TongChenTongChen
31529
One method use Java 8 Stream and lambda function:
String format = "In class %s %s with roll number %d";
List<String> result = new ArrayList<>();
outerMap.entrySet().stream()
.forEach(v -> {
String className = v.getKey();
v.getValue().entrySet().stream()
.forEach(stringStudentEntry -> result.add(String.format(format,className,stringStudentEntry.getKey(),stringStudentEntry.getValue().getRollNumber())));
});
answered Jan 17 at 5:34
TongChenTongChen
31529
answered Jan 17 at 5:34
TongChenTongChen
31529
answered Jan 17 at 5:34
TongChenTongChen
31529
answered Jan 17 at 5:34
TongChenTongChen
31529
31529
add a comment |
add a comment |
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