How do I create two different compliementary lists using same input
In my previous question - How to filter the age while grouping in map with list I was able to find the name to age groups using List<User> users. Now I am trying to find the different User groups from ages according to the threshold. I tried this
List<User> userAboveThreshold = users.stream().filter(u -> u.getAge() > 21).collect(toList());
List<User> userBelowThreshold = users.stream().filter(u -> u.getAge() <= 21).collect(toList());
This time it works I can see using
userAboveThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
userBelowThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
But I have to access the users list again to find the complimentary list. Can this not be done simpler?
java java-stream
asked Dec 20 '18 at 13:26
ManiMani
3231420
add a comment |
In my previous question - How to filter the age while grouping in map with list I was able to find the name to age groups using List<User> users. Now I am trying to find the different User groups from ages according to the threshold. I tried this
List<User> userAboveThreshold = users.stream().filter(u -> u.getAge() > 21).collect(toList());
List<User> userBelowThreshold = users.stream().filter(u -> u.getAge() <= 21).collect(toList());
This time it works I can see using
userAboveThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
userBelowThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
But I have to access the users list again to find the complimentary list. Can this not be done simpler?
java java-stream
asked Dec 20 '18 at 13:26
ManiMani
3231420
add a comment |
In my previous question - How to filter the age while grouping in map with list I was able to find the name to age groups using List<User> users. Now I am trying to find the different User groups from ages according to the threshold. I tried this
List<User> userAboveThreshold = users.stream().filter(u -> u.getAge() > 21).collect(toList());
List<User> userBelowThreshold = users.stream().filter(u -> u.getAge() <= 21).collect(toList());
This time it works I can see using
userAboveThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
userBelowThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
But I have to access the users list again to find the complimentary list. Can this not be done simpler?
java java-stream
asked Dec 20 '18 at 13:26
ManiMani
3231420
In my previous question - How to filter the age while grouping in map with list I was able to find the name to age groups using List<User> users. Now I am trying to find the different User groups from ages according to the threshold. I tried this
List<User> userAboveThreshold = users.stream().filter(u -> u.getAge() > 21).collect(toList());
List<User> userBelowThreshold = users.stream().filter(u -> u.getAge() <= 21).collect(toList());
This time it works I can see using
userAboveThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
userBelowThreshold.forEach(u -> System.out.println(u.getName() + " " + u.getAge()));
But I have to access the users list again to find the complimentary list. Can this not be done simpler?
java java-stream
java java-stream
asked Dec 20 '18 at 13:26
ManiMani
3231420
asked Dec 20 '18 at 13:26
ManiMani
3231420
asked Dec 20 '18 at 13:26
ManiMani
3231420
asked Dec 20 '18 at 13:26
ManiMani
3231420
asked Dec 20 '18 at 13:26
ManiMani
3231420
3231420
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
List.removeAll
You can use removeAll to obtain the complimentary list.
List<User> userBelowThreshold = new ArrayList<>(users); // initiated with 'users'
userBelowThreshold.removeAll(userAboveThreshold);
Note: This would require overridden equals and hashCode implementation for User.
Collectors.partitioningBy
On the other hand, if you further want to iterate over the complete users list just once, you can use Collectors.partitioningBy as:
Map<Boolean, List<User>> userAgeMap = users.stream()
.collect(Collectors.partitioningBy(user -> user.getAge() > 21, Collectors.toList()));
List<User> userAboveThreshold = userAgeMap.get(Boolean.TRUE);
List<User> userBelowThreshold = userAgeMap.get(Boolean.FALSE);
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
1
For those concerned about the cost of using a map here, worry not,Collectors.partitioningByreturns a custom map class that stores the 2 partitions (holding the thetrueandfalsemember) directly inline.
– Alexander
Dec 20 '18 at 18:47
add a comment |
You're after the partitioningBy collector:
Map<Boolean, List<User>> result =
users.stream().collect(partitioningBy(u -> u.getAge() > 21));
Then use it as follows:
List<User> userAboveThreshold = result.get(true);
List<User> userBelowThreshold = result.get(false);
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then aHashMapfor example
– Eugene
Dec 20 '18 at 13:58
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
List.removeAll
You can use removeAll to obtain the complimentary list.
List<User> userBelowThreshold = new ArrayList<>(users); // initiated with 'users'
userBelowThreshold.removeAll(userAboveThreshold);
Note: This would require overridden equals and hashCode implementation for User.
Collectors.partitioningBy
On the other hand, if you further want to iterate over the complete users list just once, you can use Collectors.partitioningBy as:
Map<Boolean, List<User>> userAgeMap = users.stream()
.collect(Collectors.partitioningBy(user -> user.getAge() > 21, Collectors.toList()));
List<User> userAboveThreshold = userAgeMap.get(Boolean.TRUE);
List<User> userBelowThreshold = userAgeMap.get(Boolean.FALSE);
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
1
For those concerned about the cost of using a map here, worry not,Collectors.partitioningByreturns a custom map class that stores the 2 partitions (holding the thetrueandfalsemember) directly inline.
– Alexander
Dec 20 '18 at 18:47
add a comment |
List.removeAll
You can use removeAll to obtain the complimentary list.
List<User> userBelowThreshold = new ArrayList<>(users); // initiated with 'users'
userBelowThreshold.removeAll(userAboveThreshold);
Note: This would require overridden equals and hashCode implementation for User.
Collectors.partitioningBy
On the other hand, if you further want to iterate over the complete users list just once, you can use Collectors.partitioningBy as:
Map<Boolean, List<User>> userAgeMap = users.stream()
.collect(Collectors.partitioningBy(user -> user.getAge() > 21, Collectors.toList()));
List<User> userAboveThreshold = userAgeMap.get(Boolean.TRUE);
List<User> userBelowThreshold = userAgeMap.get(Boolean.FALSE);
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
1
For those concerned about the cost of using a map here, worry not,Collectors.partitioningByreturns a custom map class that stores the 2 partitions (holding the thetrueandfalsemember) directly inline.
– Alexander
Dec 20 '18 at 18:47
add a comment |
List.removeAll
You can use removeAll to obtain the complimentary list.
List<User> userBelowThreshold = new ArrayList<>(users); // initiated with 'users'
userBelowThreshold.removeAll(userAboveThreshold);
Note: This would require overridden equals and hashCode implementation for User.
Collectors.partitioningBy
On the other hand, if you further want to iterate over the complete users list just once, you can use Collectors.partitioningBy as:
Map<Boolean, List<User>> userAgeMap = users.stream()
.collect(Collectors.partitioningBy(user -> user.getAge() > 21, Collectors.toList()));
List<User> userAboveThreshold = userAgeMap.get(Boolean.TRUE);
List<User> userBelowThreshold = userAgeMap.get(Boolean.FALSE);
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
List.removeAll
You can use removeAll to obtain the complimentary list.
List<User> userBelowThreshold = new ArrayList<>(users); // initiated with 'users'
userBelowThreshold.removeAll(userAboveThreshold);
Note: This would require overridden equals and hashCode implementation for User.
Collectors.partitioningBy
On the other hand, if you further want to iterate over the complete users list just once, you can use Collectors.partitioningBy as:
Map<Boolean, List<User>> userAgeMap = users.stream()
.collect(Collectors.partitioningBy(user -> user.getAge() > 21, Collectors.toList()));
List<User> userAboveThreshold = userAgeMap.get(Boolean.TRUE);
List<User> userBelowThreshold = userAgeMap.get(Boolean.FALSE);
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
edited Dec 20 '18 at 13:37
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
answered Dec 20 '18 at 13:27
nullpointernullpointer
45.5k1096185
45.5k1096185
1
For those concerned about the cost of using a map here, worry not,Collectors.partitioningByreturns a custom map class that stores the 2 partitions (holding the thetrueandfalsemember) directly inline.
– Alexander
Dec 20 '18 at 18:47
add a comment |
1
For those concerned about the cost of using a map here, worry not,Collectors.partitioningByreturns a custom map class that stores the 2 partitions (holding the thetrueandfalsemember) directly inline.
– Alexander
Dec 20 '18 at 18:47
1
1
For those concerned about the cost of using a map here, worry not,
Collectors.partitioningBy returns a custom map class that stores the 2 partitions (holding the the true and false member) directly inline.– Alexander
Dec 20 '18 at 18:47
For those concerned about the cost of using a map here, worry not,
Collectors.partitioningBy returns a custom map class that stores the 2 partitions (holding the the true and false member) directly inline.– Alexander
Dec 20 '18 at 18:47
add a comment |
You're after the partitioningBy collector:
Map<Boolean, List<User>> result =
users.stream().collect(partitioningBy(u -> u.getAge() > 21));
Then use it as follows:
List<User> userAboveThreshold = result.get(true);
List<User> userBelowThreshold = result.get(false);
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then aHashMapfor example
– Eugene
Dec 20 '18 at 13:58
add a comment |
You're after the partitioningBy collector:
Map<Boolean, List<User>> result =
users.stream().collect(partitioningBy(u -> u.getAge() > 21));
Then use it as follows:
List<User> userAboveThreshold = result.get(true);
List<User> userBelowThreshold = result.get(false);
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then aHashMapfor example
– Eugene
Dec 20 '18 at 13:58
add a comment |
You're after the partitioningBy collector:
Map<Boolean, List<User>> result =
users.stream().collect(partitioningBy(u -> u.getAge() > 21));
Then use it as follows:
List<User> userAboveThreshold = result.get(true);
List<User> userBelowThreshold = result.get(false);
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
You're after the partitioningBy collector:
Map<Boolean, List<User>> result =
users.stream().collect(partitioningBy(u -> u.getAge() > 21));
Then use it as follows:
List<User> userAboveThreshold = result.get(true);
List<User> userBelowThreshold = result.get(false);
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
answered Dec 20 '18 at 13:26
AomineAomine
41.8k74071
41.8k74071
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then aHashMapfor example
– Eugene
Dec 20 '18 at 13:58
add a comment |
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then aHashMapfor example
– Eugene
Dec 20 '18 at 13:58
2
2
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then a
HashMap for example– Eugene
Dec 20 '18 at 13:58
@Mani well you should also know that internally it uses a specialized map with two keys only, faster look-up then a
HashMap for example– Eugene
Dec 20 '18 at 13:58
add a comment |
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