The following is a minor variant of the function uniqueTuples as given by Simon Woods in this answer.

g[lists___List] := Module[{f},
  f[___, x_, x_,___] := Sequence[];
  f[x___] := (f[x]=Sequence[];{x});
  Flatten[Outer[f, lists], Length[{lists}]-1]]

data=RandomInteger[40, {6,11}];
Length[g @@ data] // Timing
(* {6.177640,388897} *)

In the definition of g we have a local variable f, which is used as a function and for which a lot of DownValues could be created. This function is not removed when the Module is evaluated:

(* {f$,f$342} *)

(* 388899 *)

I am using version 10.0.2 on Windows (32-bit). Indeed, this bug made Mathematica crash due to lack of memory when I used this function a number of times with larger arguments.

g[lists___List] := Module[{f}, f[___, x_, x_, ___] := Sequence[];
  f[x___] := (f[x] = Sequence[]; {x});
  Attributes[f] = {Orderless, Temporary};
  Flatten[Outer[f, lists], Length[{lists}] - 1]]

To address the comments let me put it another way: If you overwrite the attributes of course they are going to be 'lost'

Look at this:

g[lists___List] := Module[{f}, f[___, x_, x_, ___] := Sequence[];
  f[x___] := (f[x] = Sequence[]; {x});
  Attributes[f] = {Orderless};
  Flatten[Outer[f, lists], Length[{lists}] - 1]]
| improve this answer | |
  • 2
    $\begingroup$ Thank you very much. This is a nice and useful workaround, but adding the attribute Temporary to a local variable of a Module should be superfluous. $\endgroup$ – Fred Simons Jan 20 '15 at 10:21
  • 1
    $\begingroup$ Ah, I see. It is not a bug in Mathematica, but a subtle error of mine. The solution is to use SetAttributes[f, Orderless]; instead of defining Attributes[f]={Orderless};. Many thanks again. $\endgroup$ – Fred Simons Jan 20 '15 at 12:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.