I need to write some kind of loop that can count the frequency of each letter in a string.
For example: "aasjjikkk" would count 2 'a', 1 's', 2 'j', 1 'i', 3 'k'. Ultimately id like these to end up in a map with the character as the key and the count as the value. Any good idea how to do this?
How to count frequency of characters in a string?
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27 Answers
Using the stream API as of JDK-8:
Map<Character, Long> frequency =
str.chars()
.mapToObj(c -> (char)c)
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
or if you want the keys as Integers:
Map<Character, Integer> frequency =
str.chars()
.mapToObj(c -> (char)c)
.collect(Collectors.groupingBy(Function.identity(), Collectors.summingInt(c -> 1)));
Another variant:
Map<Character, Integer> frequency =
str.chars()
.mapToObj(c -> (char)c)
.collect(Collectors.toMap(Function.identity(), c -> 1, Math::addExact));
Since there was no Java 8 solution, thought of posting one. Also, this solution is much neater, readable and concise than some of the other solutions mentioned here.
String string = "aasjjikkk";
Map<Character, Long> characterFrequency = string.chars() // creates an IntStream
.mapToObj(c -> (char) c) // converts the IntStream to Stream<Character>
.collect(Collectors.groupingBy(c -> c, Collectors.counting())); // creates a
// Map<Character, Long>
// where the Long is
// the frequency
String s = "aaaabbbbcccddddd";
Map<Character, Integer> map = new HashMap<>();
Using one line in Java8
s.chars().forEach(e->map.put((char)e, map.getOrDefault((char)e, 0) + 1));
There is one more option and it looks quite nice. Since java 8 there is new method merge java doc
public static void main(String[] args) {
String s = "aaabbbcca";
Map<Character, Integer> freqMap = new HashMap<>();
for (int i = 0; i < s.length(); i++) {
Character c = s.charAt(i);
freqMap.merge(c, 1, (a, b) -> a + b);
}
freqMap.forEach((k, v) -> System.out.println(k + " and " + v));
}
Or even cleaner with ForEach
for (Character c : s.toCharArray()) {
freqMapSecond.merge(c, 1, Integer::sum);
}
Please try the given code below, hope it will helpful to you,
import java.util.Scanner;
class String55 {
public static int frequency(String s1,String s2)
{
int count=0;
char ch[]=s1.toCharArray();
char ch1[]=s2.toCharArray();
for (int i=0;i<ch.length-1; i++)
{
int k=i;
int j1=i+1;
int j=0;
int j11=j;
int j2=j+1;
{
while(k<ch.length && j11<ch1.length && ch[k]==ch1[j11])
{
k++;
j11++;
}
int l=k+j1;
int m=j11+j2;
if( l== m)
{
count=1;
count++;
}
}
}
return count;
}
public static void main (String[] args) {
Scanner sc=new Scanner(System.in);
System.out.println("enter the pattern");
String s1=sc.next();
System.out.println("enter the String");
String s2=sc.next();
int res=frequency(s1, s2);
System.out.println("FREQUENCY==" +res);
}
}
SAMPLE OUTPUT: enter the pattern man enter the String dhimanman FREQUENCY==2
Thank-you.Happy coding.
package com.dipu.string;
import java.util.HashMap;
import java.util.Map;
public class RepetativeCharInString {
public static void main(String[] args) {
String data = "aaabbbcccdddffffrss";
char[] charArray = data.toCharArray();
Map<Character, Integer> map = new HashMap<>();
for (char c : charArray) {
if (map.containsKey(c)) {
map.put(c, map.get(c) + 1);
} else {
map.put(c, 1);
}
}
System.out.println(map);
}
}
*import java.util.ArrayList;
import java.util.Collections;
public class Freq {
public static void main(String[] args) {
// TODO Auto-generated method stub
String temp="zsaaqaaaaaaaabbbbbcc";
List<String> temp1= new ArrayList<String> ();
ArrayList<Integer>freq=new ArrayList<Integer>();
for(int i=0;i<temp.length()-1;i++)
{
temp1.add(Character.toString(temp.charAt(i)));
}
Set<String> uniqset=new HashSet<String>(temp1);
for(String s:uniqset)
{
freq.add(Collections.frequency(temp1, s));
System.out.println(s+" -->>"+Collections.frequency(temp1, s));
}
}
}
------Output-------
a -->>10
b -->>5
c -->>1
q -->>1
s -->>1
z -->>1
Use collections frequency method to count frequency of char*
Uffh. Don't you think this is the simplest solution?
char inputChar = '|';
int freq = "|fd|fdfd|f dfd|fd".replaceAll("[^" + inputChar +"]", "").length();
System.out.println("freq " + freq);
We can use frequency method of Collections class for this. Split the string into string array. Use HashSet to remove duplicates and check frequency of each object in HashSet using frequency method of Collections
void usingCollections(){
String input = "cuttack";
String [] stringArray = input.split("");
Set<String> s = new HashSet(Arrays.asList(stringArray));
for(String abc : s){
System.out.println (abc + ":"+Collections.frequency(Arrays.asList(stringArray),abc));
}
}
This is more Effective way to count frequency of characters in a string
public class demo {
public static void main(String[] args) {
String s = "babdcwertyuiuygf";
Map<Character, Integer> map = new TreeMap<>();
s.chars().forEach(e->map.put((char)e, map.getOrDefault((char)e, 0) + 1));
StringBuffer myValue = new StringBuffer();
String myMapKeyValue = "";
for (Map.Entry<Character, Integer> entry : map.entrySet()) {
myMapKeyValue = Character.toString(entry.getKey()).concat(
Integer.toString(entry.getValue()));
myValue.append(myMapKeyValue);
}
System.out.println(myValue);
}
}
Another way using map merge method
Map<Character, Integer> map = new HashMap<>();
String s = "aasjjikkk";
for (int i = 0; i < s.length(); i++) {
map.merge(s.charAt(i), 1, (l, r) -> l + r);
#From C language
#include<stdio.h>`
#include <string.h>`
int main()
{
char s[1000];
int i,j,k,count=0,n;
printf("Enter the string : ");
gets(s);
for(j=0;s[j];j++);
n=j;
printf(" frequency count character in string:\n");
for(i=0;i<n;i++)
{
count=1;
if(s[i])
{
for(j=i+1;j<n;j++)
{
if(s[i]==s[j])
{
count++;
s[j]='\0';
}
}
printf(" '%c' = %d \n",s[i],count);
}
}
return 0;
}
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