Method if_then

src/matrix.rs:768–775

(&self, prd: F, tr: T, fa: T)

    }

    pub fn if_then<F>(&self, prd: F, tr: T, fa: T) -> Matrix<T> 
        where F: Fn(&T) -> bool {

        Matrix::from_iter(
            self.values().map(|x| if prd(x) { tr.clone() } else { fa.clone() }), 
            self.cols()
        ).unwrap()
    }
}

// --------------- Iterators ----------------------------------------