Hello I have to group by multiple fields and make a summary by one of these files, thereafter I have to work with this result and make some more transformations my problem is that I'm getting a complex structure after the grouping and it's not easy to work with this items. This is my code:
Map<String, Map<String, Map<LocalDateTime, Map<String, Double>>>> processed = null;
processed = itemsToProcess
.stream()
.collect(groupingBy(entity::getId,
groupingBy(entity::getType,
groupingBy(entity::getCreateDate,
groupingBy(entity::getCode,
summingDouble(entity::getPay))))));
The objective of this grouping is the summary of the pays but thereafter I I have to do some transformations with this processed structure, my doubt if is there is a way to transform this in a simple list in order to make more easy this task?
My input is basically a list of:
List<Person> itemsToProcess= new ArrayList<>();
#JsonInclude
public class Person extends Entity<Person > {
private static final long serialVersionUID = 1L;
/* File line content */
private String id;
private String type;
private LocalDateTime createDate;
private String code;
private double pay;
private String city
private String company
}
The output that I'm looking for is the summary of the pay field grouped by {id,type,createDate,pay}
example if I have the next values
Id type createdDAte Code pay more fields....
1 0 today BC 500
1 0 today BC 600
2 0 today BC 600
2 0 today BC 300
3 0 today BC 300
The result must be:
Id type createdDAte Code pay more fields....
1 0 today BC 1100
2 0 today BC 900
3 0 today BC 300
You can use Collectors.toMap to Map by that four properties and merging the same group person objects and creating a new one using the constructor.
List<Person> processed =
new ArrayList<>(
itemsToProcess
.stream()
.collect(Collectors.toMap(
i -> Arrays.asList(i.getId(), i.getType(), i.getCreateDate(), i.getCode()),
i -> i,
(a, b) -> new Person(a.getId(), a.getType(), a.getCreateDate(), a.getCode(),
a.getPay() + b.getPay())))
.values());
Output:
Person [id=2, type=0, createDate=2020-08-18T12:26:15.616034800, code=BC, pay=900.0]
Person [id=3, type=0, createDate=2020-08-18T12:26:15.616034800, code=BC, pay=300.0]
Person [id=1, type=0, createDate=2020-08-18T12:26:15.616034800, code=BC, pay=1100.0]
Demo here
Quick way is to group by a map of the key fields:
groupingBy(e -> Map.<String, Object>of(
"id", e.getId(),
"type", e.getType(),
"createDate", e.getCreateDate(),
"code", e.getCode(),
"pay", e.getPay()
), identity())
Map's equals() method works as you would hope it does.
Related
Context :
Consider following entity in spring boot project,
#Entity
public class Transaction{
#Id
private Integer tId;
private Integer amount;
private LocalDate invoiceDate;
private LocalDate tDate;
}
A method which creates object of transaction, doesn't set tDate.
There is an independent method which sets tDate.
So, in the database some entries don't have 'tDate'.
Problem :
Now, I want to show all the entries in database sorted using tDate but, for those entries which does not contain tDate it should consider invoiceDate.
Sample Database entries
t_id
amount
invoice_date
t_date
1
1200
2/3/2022
4/3/2022
2
2434
5/3/2022
6/3/2022
3
234
3/3/2022
NULL
Sample expected Output
[[tId = 3, amount = 234, invoiceDate = 3/3/2022, tDate = NULL]
[tId = 1, amount = 1200, invoiceDate = 2/3/2022, tDate = 4/3/2022]
[tId = 2, amount = 2434, invoiceDate = 5/3/2022, tDate = 6/3/2022]]
Note : Highlighted dates above are the dates considered for sorting.
What I tried
I tried to use the combination of nullsLast(Comparator.naturalOrder()) and thenComparing() methods of Comparator.comparing() but it doesn't give the expected output. It sorts the entries withtDate and entries without tDate separately.
Thank you in advance for any help!!
Also, I'm using MongoRepository in repository layer, so I can use the Sort object as well.
Thank you!
There are 2 sets, the user has a lot of fields, but the necessary one is the departmentId, they also gave me an id array for deletion, and this and that Strig. How can you iterate over oldUser and leave only those users whose departmentId is in removeUserById? Below is the stream that I wrote But it does not work, all users go to the abс set without exceptions
Set<User> oldEmploee = userRepository.findAllByDepartmentId(departmentId);
Set<String> newEmploee = command.getEmployees();
Set<User> abc = oldEmploee.stream().filter(e -> !newEmploee.contains(e.getDepartmentId())).collect(Collectors.toSet());
abc.forEach(user -> user.setDepartmentId("3a9b4a8a-9e8c-4b72-b3cd-4e72090c259b"));
userRepository.saveAll(abc);
Set<User> abc = oldEmploee.stream().filter(e -> newEmploee.contains(**e.getId()**)).collect(Collectors.toSet());
I use Spring JdbcTemplate to query list of several values:
List<String[]> tankNames = jdbcTemplate.queryForList(
"select name, country, level from tanklist", String[].class);
get the following error:
org.springframework.jdbc.IncorrectResultSetColumnCountException:
Incorrect column count: expected 1, actual 3
Why it expects 1 as I use String[]?
How I can get a list of values of several columns (maybe in an array of Strings) without creating an object of these 3 values?
My final goal to transform this response to a list of strings.
You can use following method instead to simplify your implementation
<T> List<T> query(String sql, RowMapper<T> rowMapper)
If you want to get list of String array (String[]) i.e. columns of each row are elements of a String array, use following
List<String[]> allTankNames = jdbcTemplate.query(
"select name, country, level from tanklist",
(rs, rowNum) -> new String[] {rs.getString(1), rs.getString(2), rs.getString(3)});
However, your code suggests you want to get one string per row having concatenated all columns, for that, use following
List<String> allTankNames = jdbcTemplate.query(
"select name, country, level from tanklist",
(rs, rowNum) -> String.format("%s %s %s", rs.getString(1),rs.getString(2), rs.getString(3)));
I did the following:
List<Map<String, Object>> allTankNames = jdbcTemplate.queryForList(
"select name, country, level from tanklist");
My goal was to transform this into a list of strings:
List<String> tankNamesWithInfo = allTankNames.stream().map(m -> (String) m.get("name") + m.get("country") + m.get("level")).collect(Collectors.toList());
I have a List of Objects called md. Each of this objects has an activityName, a startTime and an endTime(for the activity).
I want to iterate over this list and for each activity, get the startTime and endTime.
Map<String,Long> m1 = new HashMap<String,Long>();
m1 = md
.stream()
.map(s->s.activityName)
.collect(HashMap<String,Long>::new,
(map,string)->{
String d1 = md.get(md.indexOf(string)).startTime;
String d2 = md.get(md.indexOf(string)).endTime;
.
.
.
},HashMap<String,Long>::putAll);
It gives me java.lang.ArrayIndexOutOfBoundsException: -1 when I try to get the index of string String d1 = md.get(md.indexOf(string)).startTime;
Is there any other way to simplify the code using Lambda expressions?
What if I have two activities with the same name (Drinking for ex).Will it only return the index of the first Drinking activity it finds?
It seems that you are missing that fact that once you do:
md.stream().map(s -> s.activityName)
your Stream has become Stream<String>; while your md is still List<YourObject>
And in the map operation you are trying to find a String inside md, this obviously does not exist, thus a -1.
So you need a Map<String, Long> that is activitaName -> duration it takes(could be Date/Long)
md.stream()
.collect(Collectors.toMap(s -> s.activityName, x -> {
Date start = // parse s.startTime
Date end = // parse s.endTime
return end.minus(start);
}));
Now the parsing depends on the dates you use.
We are using 3 lists ListA,ListB,ListC to keep the marks for 10 students in 3 subjects (A,B,C).
Subject B and C are optional, so only few students out of 10 have marks in those subjects
Class Student{
String studentName;
int marks;
}
ListA has records for 10 students, ListB for 5 and ListC for 3 (which is also the size of the lists)
Want to know how we can sum up the marks of the students for their subjects using java 8 steam.
I tried the following
List<Integer> list = IntStream.range(0,listA.size() -1).mapToObj(i -> listA.get(i).getMarks() +
listB.get(i).getMarks() +
listC.get(i).getMarks()).collect(Collectors.toList());;
There are 2 issues with this
a) It will give IndexOutOfBoundsException as listB and listC don't have 10 elements
b) The returned list if of type Integer and I want it to be of type Student.
Any inputs will be very helpful
You can make a stream of the 3 lists and then call flatMap to put all the lists' elements into a single stream. That stream will contain one element per student per mark, so you will have to aggregate the result by student name. Something along the lines of:
Map<String, Integer> studentMap = Stream.of(listA, listB, listC)
.flatMap(Collection::stream)
.collect(groupingBy(student -> student.name, summingInt(student -> student.mark)));
Alternatively, if your Student class has getters for its fields, you can change the last line to make it more readable:
Map<String, Integer> studentMap = Stream.of(listA, listB, listC)
.flatMap(Collection::stream)
.collect(groupingBy(Student::getName, summingInt(Student::getMark)));
Then check the result by printing out the studentMap:
studentMap.forEach((key, value) -> System.out.println(key + " - " + value));
If you want to create a list of Student objects instead, you can use the result of the first map and create a new stream from its entries (this particular example assumes your Student class has an all-args constructor so you can one-line it):
List<Student> studentList = Stream.of(listA, listB, listC)
.flatMap(Collection::stream)
.collect(groupingBy(Student::getName, summingInt(Student::getMark)))
.entrySet().stream()
.map(mapEntry -> new Student(mapEntry.getKey(), mapEntry.getValue()))
.collect(toList());
I would do it as follows:
Map<String, Student> result = Stream.of(listA, listB, listC)
.flatMap(List::stream)
.collect(Collectors.toMap(
Student::getName, // key: student's name
s -> new Student(s.getName(), s.getMarks()), // value: new Student
(s1, s2) -> { // merge students with same name: sum marks
s1.setMarks(s1.getMarks() + s2.getMarks());
return s1;
}));
Here I've used Collectors.toMap to create the map (I've also assumed you have a constructor for Student that receives a name and marks).
This version of Collectors.toMap expects three arguments:
A function that returns the key for each element (here it's Student::getName)
A function that returns the value for each element (I've created a new Student instance that is a copy of the original element, this is to not modify instances from the original stream)
A merge function that is to be used when there are elements that have the same key, i.e. for students with the same name (I've summed the marks here).
If you could add the following copy constructor and method to your Student class:
public Student(Student another) {
this.name = another.name;
this.marks = another.marks;
}
public Student merge(Student another) {
this.marks += another.marks;
return this;
}
Then you could rewrite the code above in this way:
Map<String, Student> result = Stream.of(listA, listB, listC)
.flatMap(List::stream)
.collect(Collectors.toMap(
Student::getName,
Student::new,
Student::merge));