Is there any efficient way to have a case insensitive string as a HashMap key?

Question

I'm trying to count number of times a word appears in a text. I'm using HashMap and my implementation ignores case. I achieve that by converting all words to lowercase:

for line in reader.lines() {
    for mut curr in line.as_ref().unwrap().split_whitespace() {
        match word_map.entry(curr.to_string().to_lowercase()) {
            Entry::Occupied(entry) => {
                *entry.into_mut() += 1;
            }
            Entry::Vacant(entry) => {
                entry.insert(1);
            }
        }
    }
}

I want to consider "the" and "The" same, but if "the" doesn't appear just hold "The" in the HashMap. Right now, I hold all words in lowercase. Is there any efficient way to do this?

Answer 1

The easiest way to do it is to use UniCase as a key:

use unicase::UniCase;

type Words = std::collections::HashMap<UniCase, u32>;

If I understand their documentation, UniCase::new("The") stores the actual string "The" in it, but if you compare it with Unicase::new("the"), you will see that it is the same string.