I have an XML file in which I need to find and count the appearance of year tag. For example:
Found year 2020 10 times.
Found year 2017 1 times.
Found year 2019 2 times.
(...)
To avoid the duplications of the years I used HashSet. Code:
public class Publications {
public static void main(String[] args) throws IOException {
Set<String> publicationYears = new LinkedHashSet<>();
try (BufferedReader reader = Files.newBufferedReader(Paths.get("dblp-2020-04-01.xml"))) {
Pattern pattern = Pattern.compile("<year>(.+?)</year>", Pattern.DOTALL);
for (String line; (line = reader.readLine()) != null; ) {
Matcher matcher = pattern.matcher(line);
if (matcher.find()) {
String year = matcher.group(1);
publicationYears.add(year);
}
}
}
Results:
2010
2002
1992
1994
1993
2006(...)
But now I can't find an efficient code to count the appearance of each year. Creating an multidimensional array and then searching would be very slow. Any suggestions?
Try this:
count.compute(year, (k,v)->v == null ? 1 : v + 1);
Map<String, Integer> count = new LinkedHashMap<>();
try (BufferedReader reader = Files.newBufferedReader(Paths.get("dblp-2020-04-01.xml"))) {
Pattern pattern = Pattern.compile("<year>(.+?)</year>", Pattern.DOTALL);
for (String line; (line = reader.readLine()) != null; ) {
Matcher matcher = pattern.matcher(line);
if (matcher.find()) {
String year = matcher.group(1);
count.compute(year, (k,v)->v == null ? 1 : v + 1);
}
}
}
}
To print them out, do the following
count.entrySet().forEach(System.out::println);
There are so many ways to do it. Some of them are given below:
List
and use Collections.frequency
as follows:import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
public class Main {
public static void main(String[] args) {
List<Integer> years = List.of(2010, 2011, 2013, 2010, 2012, 2010, 2011, 2010, 2014);
Set<Integer> yearSet = new LinkedHashSet<Integer>(years);
for (Integer year : yearSet) {
System.out.println("Found year " + year + " " + Collections.frequency(years, year) + " times");
}
}
}
Output:
Found year 2010 4 times
Found year 2011 2 times
Found year 2013 1 times
Found year 2012 1 times
Found year 2014 1 times
List
and then create a Map
of frequency as follows:import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class Main {
public static void main(String[] args) {
List<Integer> years = List.of(2010, 2011, 2013, 2010, 2012, 2010, 2011, 2010, 2014);
Map<Integer, Integer> frequencyMap = new LinkedHashMap<Integer, Integer>();
for (Integer year : years) {
if (frequencyMap.get(year) == null) {
frequencyMap.put(year, 1);
} else {
frequencyMap.put(year, frequencyMap.get(year) + 1);
}
}
for (Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
System.out.println("Found year " + entry.getKey() + " " + entry.getValue() + " times");
}
}
}
Output:
Found year 2010 4 times
Found year 2011 2 times
Found year 2013 1 times
Found year 2012 1 times
Found year 2014 1 times
List
and then create a Map
of frequency by using Map::merge
as follows:import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class Main {
public static void main(String[] args) {
List<Integer> years = List.of(2010, 2011, 2013, 2010, 2012, 2010, 2011, 2010, 2014);
Map<Integer, Integer> frequencyMap = new LinkedHashMap<Integer, Integer>();
years.forEach(year -> frequencyMap.merge(year, 1, (oldValue, newValue) -> oldValue + newValue));
for (Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
System.out.println("Found year " + entry.getKey() + " " + entry.getValue() + " times");
}
}
}
Output:
Found year 2010 4 times
Found year 2011 2 times
Found year 2013 1 times
Found year 2012 1 times
Found year 2014 1 times
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