Getting the index length of a particular struct type

I have a custom Struct that consists of two i32 types that make out a 2D vector. I have been accessing certain indices using for loops, but I have yet to figure out how to get the length of either ‘col or ‘row’. Here’s my code:

#[derive(Debug)]
pub struct Vec2d {
    col: i32,
    row: i32,
}


fn main() {
    let mut vec_struct = Vec::new();

    for i in 0..5 {
        for j in 0..7 {  
            let index = [
                Vec2d {
                    col: j * 3,
                    row: i * 5,
                },
            ];
            vec_struct.push(index);
        }
    }

    // I want to get 5 or 7 somehow, but none of these two work
    println!("{}", vec_struct[0][0].len());
    println!("{}", vec_struct[0].len());
    
    // This works, but prints both dimensions (output: 35)
    println!("{}", vec_struct.len());
}

>Solution :

Since you’re storing your elements in a flat Vec, you’ve lost the information of where each column/row starts and ends.

You can either store them in a nested Vec<Vec<Vec2d>>, or try to restore this information armed with the knowledge that a new column starts when the column number is zero:

let columns = vec_struct
    .iter()
    .enumerate()
    .skip(1) // The first column is always zero, skip it
    .find_map(|(i, Vec2d { col, .. })| if *col == 0 { Some(i) } else { None })
    .unwrap();
let rows = vec_struct.len() / columns;

You stored the elements in one-element array ([Vec2d { ... }]). I guess you tried to do the first solution, but this array will always stay one-element-sized. You need to use a vector like that:

for i in 0..5 {
    let mut row = Vec::new();
    for j in 0..7 {
        let index = Vec2d {
            col: j * 3,
            row: i * 5,
        };
        row.push(index);
    }
    vec_struct.push(row);
}
let rows = vec_struct.len();
let columns = vec_struct[0].len();