Taking the first letter of each word

String str is given which contains lowercase English letters and spaces. It may contain multiple spaces. Get the first letter of every word and return the result as a string. The result should not contain any space.

Examples: 

Input : str = "geeks for geeks"
Output : gfg

Input : str = "geeks for geeks""
Output : hc

Source: https://www.geeksforgeeks.org/amazon-interview-set-8-2/

The idea is to traverse each character of string str and maintain a boolean variable, which was initially set as true. Whenever we encounter space we set the boolean variable is true. And if we encounter any character other than space, we will check the boolean variable, if it was set as true as copy that charter to the output string and set the boolean variable as false. If the boolean variable is set false, do nothing. 

Algorithm: 

1. Traverse string str. And initialize a variable v as true.
2. If str[i] == ' '. Set v as true.
3. If str[i] != ' '. Check if v is true or not.
   a) If true, copy str[i] to output string and set v as false.
   b) If false, do nothing.

Implementation:

Time Complexity: O(n)
Auxiliary space: O(1). 

Approach 1 : Reverse Iterative Approach 

This is simplest approach to to getting first letter of every word of the string. In this approach we are using reverse iterative loop to get letter of words. If particular letter ( i ) is 1st letter of word or not is can be determined by checking pervious character that is (i-1). If the pervious letter is space (‘ ‘) that means (i+1) is 1st letter then we simply add that letter to the string. Except character at 0th position. At the end we simply reverse the string and function will return string which contain 1st letter of word of the string.

Time Complexity: O(n)
Auxiliary space: O(1). 

Approach 2: Using StringBuilder

This approach uses the StringBuilder class of Java. In this approach, we will first split the input string based on the spaces. The spaces in the strings can be matched using a regular expression. The split strings are stored in an array of strings. Then we can simply append the first character of each split string in the String Builder object.  

Implementation:

Time Complexity: O(n)
Auxiliary space: O(1). 

Another Approach: Using boundary checker, refer https://www.geeksforgeeks.org/get-first-letter-word-string-using-regex-java/

This article is contributed by Aarti_Rathi and Anuj Chauhan. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

The metacharacter “b” matches for the word boundaries and [a-zA-Z] matches one character from the English alphabet (both cases). In short, the expression b[a-zA-Z] matches one single character from the English alphabet, both cases after every word boundary.

Therefore, to retrieve the first letter of each word −

• Compile the above expression of the compile() method of the Pattern class.

• Get the Matcher object bypassing the required input string as a parameter to the matcher() method of the Pattern class.

• Finally, for each match get the matched characters by invoking the group() method.

Example

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class FirstLetterExample {
   public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter sample text: ");
      String data = sc.nextLine();
      String regex = "b[a-zA-Z]";
      //Creating a pattern object
      Pattern pattern = Pattern.compile(regex);
      //Creating a Matcher object
      Matcher matcher = pattern.matcher(data);
      System.out.println("First letter of each word from the given string: ");
      while(matcher.find()) {
         System.out.print(matcher.group()+" ");
      }
   }
}

Output

Enter sample text:
National Intelligence Agency Research & Analysis Wing
First letter of each word from the given string:
N I A R A W

If you are looking for an array formula to extract the first letter of each word in Google Sheets, find two formulas below. Among them, one is very tricky and easy to use.

To extract the first letter of each word, we usually follow the below steps in Google Sheets (I won’t follow it to write the array formula).

Let’s assume cell A2 contains the string “medium weight beam“.

I want to extract the letters “m”, “w”, and “b” and join them as an abbreviation like “mwb“.

Usually, we will solve the above problem USING SPLIT, LEFT, and JOIN as below and drag it down to apply to the string in the next row.

Steps (formula Explanation):-

1. We can use the SPLIT function to split the string into three parts based on the space delimiter.

=split(A2," ")

2. Then using the LEFT function, we can extract the first letter from each word.

=ArrayFormula(left(split(A2," "),1))

I’ve used the ArrayFormula within the above formula since we want to extract the first letter from more than one (split) word.

3. Just combine the result.

=JOIN("",ArrayFormula(left(split(A2," "),1)))

It is advisable to wrap the formula with IFERROR to avoid error incase of no values in A2.

The above is the best non-array method to extract the first letter of each word in Google Sheets.

But this formula has one problem.

Since we have used the JOIN function, we may find it difficult to code an array formula following the above method.

We can only use part of the formula that I’ll explain later.

Here I have two alternative solutions to the above problem. One is very tricky and easy to use than the above non-array one.

I’ve two formulas below titled Array Formula 1 and Array Formula 2.

I am recommending the array formula 1.

If you are not concerned about the case sensitivity of the extracted letters, use it. It is the easiest way to extract the first letter of each word in Google Sheets.

The Array Formula 1 will convert all the extracted letters to CAPS. If you want, you can make it SMALL (lower case).

Use the Array Formula 2 if you are looking for a case sensitive formula. I mean, the extracted letters will be the same as in the string. It won’t change the letters’ case.

Array Formula 1

Let’s consider the same string in cell A2, which is “medium weight beam”.

Here is the easiest way to abbreviate the above string in Google Sheets.

Steps:-

1. Use the PROPER function to make the first letter of each word capital and the rest of the letters small.

=proper(A2)

The result will be “Medium Weight Beam”.

2. Using REGEXREPLACE, we can extract only the capital letters from the above string.

=REGEXREPLACE(proper(A2),"[^A-Z]+","")

Since it doesn’t contain the JOIN function, we can easily make it an array formula.

=ArrayFormula(REGEXREPLACE(proper(A2:A),"[^A-Z]+",""))

Array Formula 2

To get one more array formula to extract the first letter of each word in Google Sheets, please follow the steps below.

Here, we will SPLIT the strings, then extract the first letter using LEFT. Instead of JOIN, we will use the QUERY to combine the extracted letters.

1. Let’s first FILTER the range A2:A to skip blank rows.

=filter(A2:A,A2:A<>"")

2. Split the filtered strings.

=ArrayFormula(split(filter(A2:A,A2:A<>"")," "))

3. Let’s extract the first letter in each word.

=ArrayFormula(left(split(filter(A2:A,A2:A<>"")," "),1))

4. Using the QUERY, we can combine the extracted letters. I’ve got a detailed tutorial on the use of QUERY for joining strings here – The Flexible Array Formula to Join Columns in Google Sheets.

How it works?

We can use the HEADER of QUERY for this. We will use an arbitrarily large number in the header. So, the QUERY will consider all the rows in the range are headers and combine them into a single row.

4.1. Use TRANSPOSE to change the orientation of the above formula result.

=TRANSPOSE(ArrayFormula(left(split(filter(A2:A,A2:A<>"")," "),1)))

4.2. Use the QUERY to combine the letters.

=query(transpose(ArrayFormula(left(split(filter(A2:A,A2:A<>"")," "),1))),,9^9)

4.3. Again transpose it.

=transpose(query(transpose(ArrayFormula(left(split(filter(A2:A,A2:A<>"")," "),1))),,9^9))

The above is the array formula to extract the first letter from each word in Google Sheets.

But wait. See the results. The Query leaves white spaces between the joined letters.

You can use REGEXREPLACE or SUBSTITUTE to remove them.

=ArrayFormula(substitute(transpose(query(transpose(left(split(filter(A2:A,A2:A<>"")," "),1)),,9^9))," ",""))

Note:- If you have blank cells between the values in A2:A, use the below formula. In this formula, I have omitted the FILTER and included IFERROR after the SPLIT.

=ArrayFormula(substitute(transpose(query(transpose(left(iferror(split(A2:A," ")),1)),,9^9))," ",""))

I hope you could understand how to extract the first letter of each word in Google Sheets.

Thanks for the stay. Enjoy!