NonCommutativeCollect
NonCommutativeCollect[expr, x]
NonCommutativeCollect[expr, x, alg]
NonCommutativeCollect[expr, {x1, x2, ...}, alg]collects terms involving the same powers and positions of objects matching x in a non-commutative polynomial. A list of objects is collected successively.
Example
expr = x ** x ** y ** x + 2 x ** x ** z ** x +
3 x ** y ** x ** x + 4 x ** z ** x ** x;
NonCommutativeCollect[expr, x]See the official Wolfram Language reference for algebra and coefficient specifications.