Facing an error with BigDecimal question in java - java-8

Question

The problem is :
You’ve received a stream that represents a set pf laboratory samples. B before the inout data is passed on further processing, you are required to perform some pre((-)) processing on it, what you must do is:
Eliminate all null and negative values(noises).
Divide the data into triple((-)) groups of three samples and retain only complete triples.
Eliminate all triples whose average is higher that 30.
Join all triplets again.
Use SampleNormalizer to normalise the values. Unfortunately, due to poor design it returns optional<optional> and is it a bit buggy: it may return nulls(empty optionals), which you must eliminate. SampleNormalizer’s normalise method accepts a single Big Decimal.
Return a stream
You mustn’t return null.
The thing is I am supposed to solve this in java 8
`. import java.util.*;
import java.math.BigDecimal;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Stream;
import static java.math.BigDecimal.ZERO;
import static java.util.stream.Collectors.averagingDouble;
import static java.util.stream.Collectors.groupingBy;
class SamplePreprocessor {`your text`
private final SampleNormalizer normalizer;
SamplePreprocessor(SampleNormalizer normalizer) {
this.normalizer = normalizer;
}
Stream<BigDecimal> preprocess(Stream<BigDecimal> input) {
input = input.filter(bd -> bd != null && bd.compareTo(ZERO) > 0);
// Step 2: Divide the data into triple groups and filter out the ones whose average is higher than 30
input = input.collect(groupingBy(new AtomicInteger()::getAndIncrement, averagingDouble(BigDecimal::doubleValue)))
.values()
.stream()
.filter(avg -> avg.doubleValue() <= 30)
.flatMap(group -> Stream.of(group.toArray(new BigDecimal[3])))
.map(Arrays::asList)
.filter(list -> list.size() == 3)
.map(list -> list.stream().reduce(BigDecimal.ZERO, BigDecimal::add).divide(BigDecimal.valueOf(3)));
// Step 3: Use SampleNormalizer to normalize the values
input = input.map(normalizer::normalize)
.filter(Optional::isPresent)
.map(Optional::get);
// Step 4: Return the preprocessed stream of BigDecimal values
return input;
}
}
`
ERROR
Compiler output:
Starting a Gradle Daemon (subsequent builds will be faster)
Task :compileJava
/task/src/main/java/com/codility/SamplePreprocessor.java:27: error: no suitable method found for groupingBy(new Atomic[...]ement,Collector<BigDecimal,CAP#1,Double>)
input = input.collect(groupingBy(new AtomicInteger()::getAndIncrement, averagingDouble(BigDecimal::doubleValue)))
^
method Collectors.<T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>) is not applicable
(cannot infer type-variable(s) T#1,K#1,D#1,A#1,M
(actual and formal argument lists differ in length))
method Collectors.<T#2,K#2,A#2,D#2>groupingBy(Function<? super T#2,? extends K#2>,Collector<? super T#2,A#2,D#2>) is not applicable
(cannot infer type-variable(s) T#2,K#2,A#2,D#2
(argument mismatch; invalid method reference
method getAndIncrement in class AtomicInteger cannot be applied to given types
required: no arguments
found: T#2
reason: actual and formal argument lists differ in length))
method Collectors.<T#3,K#3>groupingBy(Function<? super T#3,? extends K#3>) is not applicable
(cannot infer type-variable(s) T#3,K#3
(actual and formal argument lists differ in length))
where T#1,K#1,D#1,A#1,M,T#2,K#2,A#2,D#2,T#3,K#3 are type-variables:
T#1 extends Object declared in method <T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>)
K#1 extends Object declared in method <T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>)
D#1 extends Object declared in method <T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>)
A#1 extends Object declared in method <T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>)
M extends Map<K#1,D#1> declared in method <T#1,K#1,D#1,A#1,M>groupingBy(Function<? super T#1,? extends K#1>,Supplier,Collector<? super T#1,A#1,D#1>)
T#2 extends Object declared in method <T#2,K#2,A#2,D#2>groupingBy(Function<? super T#2,? extends K#2>,Collector<? super T#2,A#2,D#2>)
K#2 extends Object declared in method <T#2,K#2,A#2,D#2>groupingBy(Function<? super T#2,? extends K#2>,Collector<? super T#2,A#2,D#2>)
A#2 extends Object declared in method <T#2,K#2,A#2,D#2>groupingBy(Function<? super T#2,? extends K#2>,Collector<? super T#2,A#2,D#2>)
D#2 extends Object declared in method <T#2,K#2,A#2,D#2>groupingBy(Function<? super T#2,? extends K#2>,Collector<? super T#2,A#2,D#2>)
T#3 extends Object declared in method <T#3,K#3>groupingBy(Function<? super T#3,? extends K#3>)
K#3 extends Object declared in method <T#3,K#3>groupingBy(Function<? super T#3,? extends K#3>)
where CAP#1 is a fresh type-variable:
CAP#1 extends Object from capture of ?
/task/src/main/java/com/codility/SamplePreprocessor.java:51: error: incompatible types: inference variable R has incompatible bounds
.map(Optional::get);
^
equality constraints: BigDecimal
lower bounds: Optional
where R,T are type-variables:
R extends Object declared in method map(Function<? super T,? extends R>)
T extends Object declared in interface Stream
2 errors
Task :compileJava FAILED
FAILURE: Build failed with an exception.
What went wrong:
Execution failed for task ':compileJava'.
Compilation failed; see the compiler error output for details.
Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
Get more help at https://help.gradle.org
Deprecated Gradle features were used in this build, making it incompatible with Gradle 5.0.
See https://docs.gradle.org/4.8.1/userguide/command_line_interface.html#sec:command_line_warnings
BUILD FAILED in 9s
1 actionable task: 1 executed
Exit code: 1