Collecting terms / factoring out multiplied terms

I'm trying to convert a cartesian line element to spherical polar line element.

I'm stuck at collecting/factoring out multiplied terms from a big equation; here's what I have so far;

LineElement = collect((dx) + (dy) + (dz), [dr,dtheta*r,r * sin(theta)*dphi]); (I have all of these defined in syms accordingly);

output: (cos(theta) + cos(phi)*sin(theta) + sin(phi)*sin(theta))*dr + dtheta*r*cos(phi)*cos(theta) - dphi*r*sin(phi)*sin(theta) - dtheta*r*sin(theta) + dphi*r*cos(phi)*sin(theta) + dtheta*r*cos(theta)*sin(phi)

dr is factored out nicely, but I want the same to happen with r*dtheta and r*sin(theta)dphi

Please help as I have no idea what I'm doing.

Answer 1

[John D'Errico]

Be serious. That is not big. There are some things (this is one of them) that are far simpler to do by pencil and paper than to use a computer.

[Zuzanna]

It's not my choice, it's an assignment. I've done it by pencil already. I'm looking for help, that's all.