Constructing list from multi level map in Java 8
6
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 1 hour ago
JoyJoy
1,09472352
add a comment |
6
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 1 hour ago
JoyJoy
1,09472352
add a comment |
6
6
6
1
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 1 hour ago
JoyJoy
1,09472352
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 1 hour ago
JoyJoy
1,09472352
asked 1 hour ago
JoyJoy
1,09472352
asked 1 hour ago
JoyJoy
1,09472352
asked 1 hour ago
JoyJoy
1,09472352
asked 1 hour ago
JoyJoy
1,09472352
1,09472352
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
4
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 1 hour ago
nullpointernullpointer
45.5k1096185
add a comment |
1
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 40 mins ago
TongChenTongChen
21529
add a comment |
1
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 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54229285%2fconstructing-list-from-multi-level-map-in-java-8%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
4
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 1 hour ago
nullpointernullpointer
45.5k1096185
add a comment |
4
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 1 hour ago
nullpointernullpointer
45.5k1096185
add a comment |
4
4
4
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 1 hour ago
nullpointernullpointer
45.5k1096185
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 1 hour ago
nullpointernullpointer
45.5k1096185
edited 27 mins ago
answered 1 hour ago
nullpointernullpointer
45.5k1096185
answered 1 hour ago
nullpointernullpointer
45.5k1096185
answered 1 hour ago
nullpointernullpointer
45.5k1096185
45.5k1096185
add a comment |
add a comment |
1
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 40 mins ago
TongChenTongChen
21529
add a comment |
1
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 40 mins ago
TongChenTongChen
21529
add a comment |
1
1
1
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 40 mins ago
TongChenTongChen
21529
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 40 mins ago
TongChenTongChen
21529
answered 40 mins ago
TongChenTongChen
21529
answered 40 mins ago
TongChenTongChen
21529
answered 40 mins ago
TongChenTongChen
21529
21529
add a comment |
add a comment |
1
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 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
add a comment |
1
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 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
add a comment |
1
1
1
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 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
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 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
edited 28 mins ago
answered 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
answered 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
answered 58 mins ago
Ravindra RanwalaRavindra Ranwala
8,71531634
8,71531634
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
add a comment |
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
1
1
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
@nullpointer Thanks for pointing that out. I have updated my answer.
– Ravindra Ranwala
39 mins ago
add a comment |
draft saved
draft discarded
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54229285%2fconstructing-list-from-multi-level-map-in-java-8%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
