Extracting attributes from a function

Question

From an expression describing a mathematical function, I would like to extract its parameters. For example, from the expression 4 Sin[2 a x^2 + b x + c], assuming that x is the function variable, I would like to have {a,b,c}.

I tried using patterns with FixedPoint and the TreeForm to select the leaves with heads corresponding to Symbol (but x), but unfortunately unsuccessfully.

This gets you most of the way there: http://mathematica.stackexchange.com/questions/21257/extracting-variables-from-an-expression — Moo, Mar 02 '16 at 22:55

Bob Hanlon · Accepted Answer · 2016-03-08T18:42:22.957

5

expr = 4 Sin[2 a π x^2 + b x + c] + d E^f;

Cases[Level[expr, {-1}], Except[x, _Symbol?(! NumericQ[#] &)]] // Union

(*  {a, b, c, d, f}  *)

Or

Cases[Level[expr, {-1}], Except[x | _?NumericQ, _Symbol]] // Union

(*  {a, b, c, d, f}  *)

edited Mar 08 '16 at 18:42

answered Mar 03 '16 at 01:00

Bob Hanlon

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Works great, thank you ! Be careful to delete duplicates if there is twice a symbol occurring. – Mammouth Mar 08 '16 at 18:39
@Mammouth - use Union instead of Sort. Modified above. – Bob Hanlon Mar 08 '16 at 18:41

Extracting attributes from a function

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