others-rust tutorials-1-how to count number of words using rust?

1. Purpose

In this post, I will try to use rust language to count the number of words in a sentence.



2. Solution

2.1 Show me the code

Talk is cheap, show me the code:

fn count_word() {
    let text = "Don't say hello to boys again, boys. Just don't say it."; // line 1
    let mut map = HashMap::new();   //line 2
    let v:Vec<&str> = text.split_terminator(&[' ', ',','.'][..]).collect(); // line 3
    for word in v {
        let count = map.entry(word.to_lowercase()).or_insert(0); // line 4
        *count+=1;  //line 5
    }
    println!("{:?}",map); // line 6
}

run the above code, we get this:

➜  rust-tutorial-1 git:(main) cargo run  
    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
     Running `target/debug/rust-tutorial-1`
{"boys": 2, "hello": 1, "don't": 2, "say": 2, "": 2, "it": 1, "to": 1, "again": 1, "just": 1}

2.2 Code explanation

  • line 1: I just declared a string literal.
    let text = "Don't say hello to boys again, boys. Just don't say it."; // line 1
    
  • line 2: I defined a HashMap
    let mut map = HashMap::new();   //line 2
    
  • line 3: This is the key point, I use the .split_termiator to split the string into words, I passed an array of terminator characters to .split_terminator, rust string will be splited by those characters. It’s awesome.
    let v:Vec<&str> = text.split_terminator(&[' ', ',','.'][..]).collect(); // line 3
    

    Some examples of .split_terminator:

    let mut split = "A..B..".split_terminator('.');
    assert_eq!(split.as_str(), "A..B..");
    split.next();
    assert_eq!(split.as_str(), ".B..");
    split.by_ref().for_each(drop);
    assert_eq!(split.as_str(), "");
    
  • line 4: I use HashMap’s .entry function to check if the word exists in the map, if not , it will be inserted to the map with the value 0, and then the reference to 0 is returned as variable count
    let count = map.entry(word.to_lowercase()).or_insert(0); // line 4
    
  • line 5: I increased the variable count,because it’s already bound to the word in the map, so the count of the word is increased.
    *count+=1;  //line 5
    
  • line 6: I use the trait ‘Debug’ of HashMap to print the key and values in the map
    println!("{:?}",map); // line 6
    

2.3 The code example is in github.com

You can find the whole code examples on github.com: rust-tutorials-1



3. Summary

In this post, I demonstrated how to count the number of words in a rust string using .split_terminator of string and .entry of HashMap. That’s it, thanks for your reading.

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