List comprehension-like workflow?

[mihirmanna]

I have lists of the masses, diameters, and heights of various aluminum cylinders and I want to calculate their respective densities. How can I achieve that using Numbat? This is what I've been trying so far.

let masses           = [85.2g,   264.3g,  438.1g,  441.7g,  441.9g]
let heights          = [0.99cm,  3.015cm, 4.99cm,  5cm,     4.99cm]
let diameters        = [6.325cm, 6.345cm, 6.350cm, 6.345cm, 6.350cm]

fn calculate_density(mass: Mass, height: Length, diameter: Length) -> MassDensity = mass / (pi*(diameter/2)^2 * height)

let rho = calculate_density(masses, heights, diameters)  # Would like to output a list of densities

But the type checker won't let me pass lists into the function. Is there a way to get around this? I'm pretty new to Numbat so I appreciate any input! Thanks 😁

[Goju-Ryu]

You can't easily do this with three lists, but if you make one list of structs each containing one mass, height and diameter, then you can use the map function to apply a function on each element.

If you need I can provide a simple example implementation of this later when I have a little more time.

[mihirmanna]

Thanks! I've implemented something like this for now:

struct Cylinder {
    mass:     Mass,
    height:   Length,
    diameter: Length,
}

let cylinders = [
    Cylinder { mass: 85.2g,  height: 0.99cm,  diameter: 6.325cm },
    Cylinder { mass: 264.3g, height: 3.015cm, diameter: 6.345cm },
    Cylinder { mass: 438.1g, height: 4.99cm,  diameter: 6.350cm },
    Cylinder { mass: 441.7g, height: 5cm,     diameter: 6.345cm },
    Cylinder { mass: 441.9g, height: 4.99cm,  diameter: 6.350cm }
]

fn density(cylinder: Cylinder) -> MassDensity = cylinder.mass / (pi*(cylinder.diameter/2)^2 * cylinder.height)

let densities = map(density, cylinders)

Which seems to do the trick.

[Goju-Ryu]

That is almost exactly the example I would have made if you had needed it 😄