@tomleslie thanks for informing me why an array should be used. I have given more explanation now, could you please take a look now?

@acer Hi, I created only one question, the other one was a comment on a related question. But I had no response from there, only then I posted my question.

@mmcdara this is great, @Carl Love code fails if I have another term in C, eg : 

C := x*u[]*u[1,2,2]^3*u[1,1,2]+u[2];

@Carl Love Much appreciated. 

@acer thanks, this should do :)

@nm great answer thanks

@Carl Love Thanks for noticing this. Such a stupid mistake!

@tomleslie  wasn't aware of the "has" command. Thank you very much.

Thank you @tomleslie. The command is working great!

@ecterrab thanks for your answer, but that command doesn't work for me. I am not working with differential polynomials.
 

@vv Yes, exactly that's what I wanted. Thank you so much. Now, I have my own normal form for polynomials :)

@vv thank you but this is not exactly what I was looking for. We need to sort and for that we need to define an order, by u[i]=v[i], I mean that the order is same, eg, u[3] has the same order as v[3] which is demonstrated in my example above that is either of them can come first.

I have a list of variables 

L1:=[d, u[1], u[3], u[5], u[7], v[1], v[3], v[5], v[6], v[7], v[9]]

Idea is to do the same thing what are you doing but

sort(f, order=plex(v[9],u[7],v[7],v[6],v[5],u[5],v[3],u[3],u[1],v[1],d) );

But this list of variables changes every time depending on the polynomial. Basically I am looking for a way to obtain this list from L1

L2:=[v[9],u[7],v[7],v[6],v[5],u[5],v[3],u[3],u[1],v[1],d]

I hope its clear. Thanks

@John Fredsted Thank you John, Later I also realised the same.

@Carl Love Thanks again for your awesome answer. Your code is working perfectly fine with the same proc function_coeffs but mine is still not working. Thats frustating :(. I still couldn't figure out what's going wrong.

@Kitonum Thank you and everyone for this overwhelming respone. I think I can work on my problem now. Thnaks again :)