fn col_map<F>(&self, f: F) -> Matrix
    where
        F: Fn(Vec<f64>) -> Vec<f64>,
    {
        let mut result = matrix(vec![0f64; self.row * self.col], self.row, self.col, Col);

        for i in 0..self.col {
            result.subs_col(i, &f(self.col(i)));
        }

        result
    }
Column map

# Example
```rust
use peroxide::fuga::*;

let x = ml_matrix("1 2;3 4;5 6");
let y = x.col_map(|c| c.fmap(|t| t - c.mean()));

assert_eq!(y, ml_matrix("-2 -2;0 0;2 2"));
```
src/structure/matrix.rs