To count the number of elements in an array matching a condition in Rust 1.55, you can use the iter() and .filter() methods to create an iterator that only includes elements that match the given condition, and then use the count() method to count the number of elements in that iterator. Here's an example:
let numbers = [1, 2, 3, 4, 5];
// count the number of even numbers in the array
let count_even = numbers.iter().filter(|&n| n % 2 == 0).count();
println!("There are {} even numbers in the array", count_even);
In this example, we first define an array of numbers. We then create an iterator over the array with the iter() method and use the .filter() method to only include elements that are even (i.e., have a remainder of 0 when divided by 2). Finally, we use the count() method to count the number of elements in the iterator. The output of this code will be:
There are 2 even numbers in the array
You can adjust the condition to count elements matching any condition you need.