Odtnhj

I have the following list:

l=2 x, x, 4 x, x, x, 2 x, 4 x, x, x, 2 x

I want to pick those elements that have coefficients bigger than 1, i.e. 2 x, 4 x, 2 x, 4 x, 2 x
I tried

Select[CoefficientList[2 x, x, 4 x, x, x, 2 x, 4 x, x, x, 2 x, 
 x][[All, 2]], # > 1 &]*x

which return what I need but I believe there must be a much shorter and faster way? Also I would like to find the position of 2 x, 4 x, 2 x, 4 x, 2 x in my original list so I did:

Position[2 x, x, 4 x, x, x, 2 x, 4 x, x, x, 2 x, 2 x, 4 x, 2 x, 
 4 x, 2 x]

which does not work so I must be wrong

l = 2 x, x, 4 x, x, x, 2 x, 4 x, x, x, 2 x;

s = Select[CoefficientList[l, x][[All, 2]], # > 1 &]*x

p = Position[l, Alternatives @@ Union[s]]

1, 3, 6, 7, 10

Extract[l, p]

You might do like this:

l /. x -> 1 /. x_ /; x == 1 -> Nothing /. a_ -> a*x
(* 2 x, 4 x, 2 x, 4 x, 2 x *)

Have fun!

You can try

Pick[l,Exponent[x,l],0] 

2 x, 4 x, 2 x, 4 x, 2 x

or

Flatten[Take[l,#]&/@Position[Exponent[x,l],0]] 

Also if you want the positions try

Position[Exponent[x, l], 0] 

1, 3, 6, 7, 10

l = 2 x, x, 4 x, -x, x, 2 x, 4 x, x, x, 2 x;
test = Clip[Coefficient[l, x], 1, 1, 1, 0]; (* 1 means coeffient <= 1, else 0 *)
l2 = Pick[l, test, 0]
pos = Ordering[test, Length[l2]]

2 x, 4 x, 2 x, 4 x, 2 x

1, 3, 6, 7, 10

l=2 x, x, 4 x, x, x, 2 x, 4 x, x, x, 2 x;
Pick[l, Unitize[D[l, x] - 1], 1]

2 x, 4 x, 2 x, 4 x, 2 x

 Flatten@Position[Unitize[D[l, x] - 1], 1]

1, 3, 6, 7, 10