I am trying to find a number of Occurrence of each character on the given string.
- Expected output:
t=2 e=1 s=1 i=1 n=1 g=1
- Current output:
T=0 e=0 s=0 t=0 i=0 n=0 g=0
Code:
String str = "Testing";
int count = 0;
Pattern p = Pattern.compile("[a-zA-Z]", Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(str);
while (m.find()) {
if (m.group().equals(str)) {
count++;
}
System.out.println(m.group() + "=" + count);
}
There are many ways of doing this but I am looking for Regex only, so how can we achieve that by using Regex. Any Help would be Appreciated. Thanks in advance.
No need for a regex to solve your problem, if you are using Java8+ you can just use :
String input = "Testing";
Map<String, Long> result = Arrays.stream(input.split(""))
.map(String::toLowerCase)
.collect(Collectors.groupingBy(s -> s, LinkedHashMap::new, Collectors.counting()));
outputs
{t=2, e=1, s=1, i=1, n=1, g=1}
Edit
mmm, Pattern in this case is useless I don't advice to use it in this problem, as an alternative solution using Pattern with results from Java9+ you can use :
String str = "Testing";
Pattern.compile(".").matcher(str)
.results()
.map(m -> m.group().toLowerCase())
.collect(Collectors.groupingBy(s -> s, LinkedHashMap::new, Collectors.counting()))
.forEach((k, v) -> System.out.println(k + " = " + v));
Outputs
t = 2
e = 1
s = 1
i = 1
n = 1
g = 1
There are a lot of ways of achieving the result, but Regex is not a tool for this one. If you want to filter the characters and assure only [a-zA-Z]
will be count, filter the unwanted characters with: string = string.replaceAll("[^a-zA-Z]", "");
. Now back to your issue.
You need to split String
to characters and a Map<Character, Integer>
you will store these characters and their number of occurrences. I suggest you use LinkedHashMap<Character, Integer>
which assures the order of the insertion.
char[] charArray = string.toCharArray();
Map<Character, Integer> map = new LinkedHashMap<>();
Now loop through the characters and save them to the map. If a character has already been stored, increment the value by one. This might be achieved with a procedural and traditional for-loop
or since Java 8 you can use java-stream.
Before Java 8:
for (char ch: charArray) {
if(map.containsKey(ch)){
map.put(ch, map.get(ch)+1);
} else {
map.put(ch, 1);
}
}
After Java 8 (string.split("")
returns an array of Strings, you need to map them to characters):
Map<Character, Long> map = Arrays
.asList(string.split("")).stream().map(s -> s.charAt(0))
.collect(Collectors.groupingBy(s -> s, LinkedHashMap::new, Collectors.counting()));
In both cases the output will be the same:
System.out.println(map); // prints {t=2, e=1, s=1, i=1, n=1, g=1}