Sorting this Map in Java
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I have a Map where FullName is an object and contains another object of class Name that contains FirstName and LastName. Firstname and last names are String. (Yes i know its a bad design, but i am trying to learn sorting)
The key String is just id's such as 1,2,3,...
I want to sort based on the full name(both firstname and last name), and just return a list of id's.
This is the code i have so far, but i am getting a syntax error on the sorted portion where i am passing the comparator. And also I am pretty sure i am doing something incorrect semantically too.
List<String> listofIds = map.entrySet().stream()
.sorted(new ValueComparator(map))
.map(Map.Entry::getKey)
.collect(toList());
class ValueComparator implements Comparator<String> {
Map<String, FullName> base;
public ValueComparator(Map<String, FullName> base) {
this.base = base;
}
public int compare(String a, String b) {
FullName fullName1 = base.get(a);
FullName fullName2 = base.get(b);
return(fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName()));
}
}
java sorting hashmap
asked Nov 16 '18 at 19:40
SaadSaad
447412
add a comment |
I have a Map where FullName is an object and contains another object of class Name that contains FirstName and LastName. Firstname and last names are String. (Yes i know its a bad design, but i am trying to learn sorting)
The key String is just id's such as 1,2,3,...
I want to sort based on the full name(both firstname and last name), and just return a list of id's.
This is the code i have so far, but i am getting a syntax error on the sorted portion where i am passing the comparator. And also I am pretty sure i am doing something incorrect semantically too.
List<String> listofIds = map.entrySet().stream()
.sorted(new ValueComparator(map))
.map(Map.Entry::getKey)
.collect(toList());
class ValueComparator implements Comparator<String> {
Map<String, FullName> base;
public ValueComparator(Map<String, FullName> base) {
this.base = base;
}
public int compare(String a, String b) {
FullName fullName1 = base.get(a);
FullName fullName2 = base.get(b);
return(fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName()));
}
}
java sorting hashmap
asked Nov 16 '18 at 19:40
SaadSaad
447412
You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48
add a comment |
I have a Map where FullName is an object and contains another object of class Name that contains FirstName and LastName. Firstname and last names are String. (Yes i know its a bad design, but i am trying to learn sorting)
The key String is just id's such as 1,2,3,...
I want to sort based on the full name(both firstname and last name), and just return a list of id's.
This is the code i have so far, but i am getting a syntax error on the sorted portion where i am passing the comparator. And also I am pretty sure i am doing something incorrect semantically too.
List<String> listofIds = map.entrySet().stream()
.sorted(new ValueComparator(map))
.map(Map.Entry::getKey)
.collect(toList());
class ValueComparator implements Comparator<String> {
Map<String, FullName> base;
public ValueComparator(Map<String, FullName> base) {
this.base = base;
}
public int compare(String a, String b) {
FullName fullName1 = base.get(a);
FullName fullName2 = base.get(b);
return(fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName()));
}
}
java sorting hashmap
asked Nov 16 '18 at 19:40
SaadSaad
447412
I have a Map where FullName is an object and contains another object of class Name that contains FirstName and LastName. Firstname and last names are String. (Yes i know its a bad design, but i am trying to learn sorting)
The key String is just id's such as 1,2,3,...
I want to sort based on the full name(both firstname and last name), and just return a list of id's.
This is the code i have so far, but i am getting a syntax error on the sorted portion where i am passing the comparator. And also I am pretty sure i am doing something incorrect semantically too.
List<String> listofIds = map.entrySet().stream()
.sorted(new ValueComparator(map))
.map(Map.Entry::getKey)
.collect(toList());
class ValueComparator implements Comparator<String> {
Map<String, FullName> base;
public ValueComparator(Map<String, FullName> base) {
this.base = base;
}
public int compare(String a, String b) {
FullName fullName1 = base.get(a);
FullName fullName2 = base.get(b);
return(fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName()));
}
}
java sorting hashmap
java sorting hashmap
asked Nov 16 '18 at 19:40
SaadSaad
447412
asked Nov 16 '18 at 19:40
SaadSaad
447412
asked Nov 16 '18 at 19:40
SaadSaad
447412
asked Nov 16 '18 at 19:40
SaadSaad
447412
asked Nov 16 '18 at 19:40
SaadSaad
447412
447412
You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48
add a comment |
You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48
You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48
add a comment |
1 Answer
1
active
oldest
votes
Your comparator is for String objects, but map.entrySet().stream() returns a stream of Entry<String, FullName> objects.
As suggested by JB in the comments, you can use the static Comparator method #comparing to quickly build a Comparator:
List<String> listofIds = map.entrySet().stream().sorted(
Comparator.comparing(e -> e.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
You can take advantage of Comparator being a functional interface like this:
List<String> listofIds = map.entrySet().stream().sorted(
(e1, e2) -> e1.getValue().getName().getFirstName().compareTo(
e2.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
If you still want to use a Comparator object, you could use:
private static class ValueComparator implements Comparator<Entry<String, FullName>> {
@Override
public int compare(Entry<String, FullName> e1, Entry<String, FullName>> e2) {
FullName fullName1 = e1.getValue();
FullName fullName2 = e2.getValue();
return fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName());
}
}
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
1
An even better solution would be to useComparator.comparing(e -> e.getValue().getName().getFirstName())
– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
active
oldest
votes
active
oldest
votes
Your comparator is for String objects, but map.entrySet().stream() returns a stream of Entry<String, FullName> objects.
As suggested by JB in the comments, you can use the static Comparator method #comparing to quickly build a Comparator:
List<String> listofIds = map.entrySet().stream().sorted(
Comparator.comparing(e -> e.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
You can take advantage of Comparator being a functional interface like this:
List<String> listofIds = map.entrySet().stream().sorted(
(e1, e2) -> e1.getValue().getName().getFirstName().compareTo(
e2.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
If you still want to use a Comparator object, you could use:
private static class ValueComparator implements Comparator<Entry<String, FullName>> {
@Override
public int compare(Entry<String, FullName> e1, Entry<String, FullName>> e2) {
FullName fullName1 = e1.getValue();
FullName fullName2 = e2.getValue();
return fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName());
}
}
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
1
An even better solution would be to useComparator.comparing(e -> e.getValue().getName().getFirstName())
– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
add a comment |
Your comparator is for String objects, but map.entrySet().stream() returns a stream of Entry<String, FullName> objects.
As suggested by JB in the comments, you can use the static Comparator method #comparing to quickly build a Comparator:
List<String> listofIds = map.entrySet().stream().sorted(
Comparator.comparing(e -> e.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
You can take advantage of Comparator being a functional interface like this:
List<String> listofIds = map.entrySet().stream().sorted(
(e1, e2) -> e1.getValue().getName().getFirstName().compareTo(
e2.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
If you still want to use a Comparator object, you could use:
private static class ValueComparator implements Comparator<Entry<String, FullName>> {
@Override
public int compare(Entry<String, FullName> e1, Entry<String, FullName>> e2) {
FullName fullName1 = e1.getValue();
FullName fullName2 = e2.getValue();
return fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName());
}
}
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
1
An even better solution would be to useComparator.comparing(e -> e.getValue().getName().getFirstName())
– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
add a comment |
Your comparator is for String objects, but map.entrySet().stream() returns a stream of Entry<String, FullName> objects.
As suggested by JB in the comments, you can use the static Comparator method #comparing to quickly build a Comparator:
List<String> listofIds = map.entrySet().stream().sorted(
Comparator.comparing(e -> e.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
You can take advantage of Comparator being a functional interface like this:
List<String> listofIds = map.entrySet().stream().sorted(
(e1, e2) -> e1.getValue().getName().getFirstName().compareTo(
e2.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
If you still want to use a Comparator object, you could use:
private static class ValueComparator implements Comparator<Entry<String, FullName>> {
@Override
public int compare(Entry<String, FullName> e1, Entry<String, FullName>> e2) {
FullName fullName1 = e1.getValue();
FullName fullName2 = e2.getValue();
return fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName());
}
}
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
Your comparator is for String objects, but map.entrySet().stream() returns a stream of Entry<String, FullName> objects.
As suggested by JB in the comments, you can use the static Comparator method #comparing to quickly build a Comparator:
List<String> listofIds = map.entrySet().stream().sorted(
Comparator.comparing(e -> e.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
You can take advantage of Comparator being a functional interface like this:
List<String> listofIds = map.entrySet().stream().sorted(
(e1, e2) -> e1.getValue().getName().getFirstName().compareTo(
e2.getValue().getName().getFirstName())
).map(Map.Entry::getKey).collect(toList());
If you still want to use a Comparator object, you could use:
private static class ValueComparator implements Comparator<Entry<String, FullName>> {
@Override
public int compare(Entry<String, FullName> e1, Entry<String, FullName>> e2) {
FullName fullName1 = e1.getValue();
FullName fullName2 = e2.getValue();
return fullName1.getName().getFirstName()
.compareTo(fullName2.getName().getFirstName());
}
}
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
edited Nov 16 '18 at 19:57
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
answered Nov 16 '18 at 19:47
lucasvwlucasvw
532822
532822
1
An even better solution would be to useComparator.comparing(e -> e.getValue().getName().getFirstName())
– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
add a comment |
1
An even better solution would be to useComparator.comparing(e -> e.getValue().getName().getFirstName())
– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
1
1
An even better solution would be to use
Comparator.comparing(e -> e.getValue().getName().getFirstName())– JB Nizet
Nov 16 '18 at 19:53
An even better solution would be to use
Comparator.comparing(e -> e.getValue().getName().getFirstName())– JB Nizet
Nov 16 '18 at 19:53
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
@JBNizet I wasn't aware of that function, nice!
– lucasvw
Nov 16 '18 at 19:55
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
I'm sure you can make the adjustment to compare both :) Maybe give it a try and if you run into trouble you can ask a new question. Glad I can help!
– lucasvw
Nov 16 '18 at 20:37
add a comment |
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You want to compare Map entries together. So what you need is a Comparator<Map.Entry<String, FullName>>, not a Comparator<String>.
– JB Nizet
Nov 16 '18 at 19:45
It would be helpful to have the code for FullName since it's used in the code you do share, and actual error. For more advice on how to write a good question, see: stackoverflow.com/help/how-to-ask
– Geoffrey Wiseman
Nov 16 '18 at 19:48