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$\begingroup$ 
 c[i_, j_] := If[OddQ[i + j] == True, Ti, Ni];
l1 = Flatten[
  Table[Flatten[{i b[[1]] + j b[[2]], c[i, j]}, 1], {i, -3, 
    3}, {j, -3, 3}], 1]
(* {{3, 0, Ni}, {3, -1, Ti}, {3, -2, Ni}, {3, -3, Ti}, {3, -4, 
  Ni}, {3, -5, Ti}, {3, -6, Ni}, {2, 1, Ti}, {2, 0, Ni}, {2, -1, 
  Ti}, {2, -2, Ni}, {2, -3, Ti}, {2, -4, Ni}, {2, -5, Ti}, {1, 2, 
  Ni}, {1, 1, Ti}, {1, 0, Ni}, {1, -1, Ti}, {1, -2, Ni}, {1, -3, 
  Ti}, {1, -4, Ni}, {0, 3, Ti}, {0, 2, Ni}, {0, 1, Ti}, {0, 0, 
  Ni}, {0, -1, Ti}, {0, -2, Ni}, {0, -3, Ti}, {-1, 4, Ni}, {-1, 3, 
  Ti}, {-1, 2, Ni}, {-1, 1, Ti}, {-1, 0, Ni}, {-1, -1, Ti}, {-1, -2, 
  Ni}, {-2, 5, Ti}, {-2, 4, Ni}, {-2, 3, Ti}, {-2, 2, Ni}, {-2, 1, 
  Ti}, {-2, 0, Ni}, {-2, -1, Ti}, {-3, 6, Ni}, {-3, 5, Ti}, {-3, 4, 
  Ni}, {-3, 3, Ti}, {-3, 2, Ni}, {-3, 1, Ti}, {-3, 0, Ni}} *)

In the above code, I want to Randomly chose n number (say 5) elements from the list l1 which contain Ni as replace that Ni by O. How do I do it?

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1 Answer 1

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4
$\begingroup$

The goal here is to use Position to make a list of the positions where Ni appears in the list, and then use RandomChoice to choose 5 and replace them using ReplacePart

list = {{3, 0, Ni}, {3, -1, Ti}, {3, -2, Ni}, {3, -3, Ti}, {3, -4, 
    Ni}, {3, -5, Ti}, {3, -6, Ni}, {2, 1, Ti}, {2, 0, Ni}, {2, -1, 
    Ti}, {2, -2, Ni}, {2, -3, Ti}, {2, -4, Ni}, {2, -5, Ti}, {1, 2, 
    Ni}, {1, 1, Ti}, {1, 0, Ni}, {1, -1, Ti}, {1, -2, Ni}, {1, -3, 
    Ti}, {1, -4, Ni}, {0, 3, Ti}, {0, 2, Ni}, {0, 1, Ti}, {0, 0, 
    Ni}, {0, -1, Ti}, {0, -2, Ni}, {0, -3, Ti}, {-1, 4, Ni}, {-1, 3, 
    Ti}, {-1, 2, Ni}, {-1, 1, Ti}, {-1, 0, Ni}, {-1, -1, Ti}, {-1, -2,
     Ni}, {-2, 5, Ti}, {-2, 4, Ni}, {-2, 3, Ti}, {-2, 2, Ni}, {-2, 1, 
    Ti}, {-2, 0, Ni}, {-2, -1, Ti}, {-3, 6, Ni}, {-3, 5, Ti}, {-3, 4, 
    Ni}, {-3, 3, Ti}, {-3, 2, Ni}, {-3, 1, Ti}, {-3, 0, Ni}};

ReplacePart[list,
 RandomChoice[Position[list, Ni], 5] -> O]
(* {{3, 0, Ni}, {3, -1, Ti}, {3, -2, Ni}, {3, -3, Ti}, {3, -4, 
  Ni}, {3, -5, Ti}, {3, -6, O}, {2, 1, Ti}, {2, 0, Ni}, {2, -1, 
  Ti}, {2, -2, Ni}, {2, -3, Ti}, {2, -4, O}, {2, -5, Ti}, {1, 2, 
  Ni}, {1, 1, Ti}, {1, 0, Ni}, {1, -1, Ti}, {1, -2, Ni}, {1, -3, 
  Ti}, {1, -4, Ni}, {0, 3, Ti}, {0, 2, O}, {0, 1, Ti}, {0, 0, 
  Ni}, {0, -1, Ti}, {0, -2, Ni}, {0, -3, Ti}, {-1, 4, Ni}, {-1, 3, 
  Ti}, {-1, 2, Ni}, {-1, 1, Ti}, {-1, 0, Ni}, {-1, -1, Ti}, {-1, -2, 
  O}, {-2, 5, Ti}, {-2, 4, Ni}, {-2, 3, Ti}, {-2, 2, Ni}, {-2, 1, 
  Ti}, {-2, 0, Ni}, {-2, -1, Ti}, {-3, 6, Ni}, {-3, 5, Ti}, {-3, 4, 
  Ni}, {-3, 3, Ti}, {-3, 2, O}, {-3, 1, Ti}, {-3, 0, Ni}} *)
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4
  • $\begingroup$ O like the letter O, right (oxygen instead of nickel)? I think that is what I have there $\endgroup$
    – Jason B.
    Commented Feb 22, 2016 at 14:31
  • $\begingroup$ My mistake, the font used confused me. I apologize. $\endgroup$
    – Bob Hanlon
    Commented Feb 22, 2016 at 14:34
  • $\begingroup$ No worries, it's really troublesome for me that the 2 keys are right next to each other, and you'd be surprised how often I type the wrong one lol $\endgroup$
    – Jason B.
    Commented Feb 22, 2016 at 14:35
  • $\begingroup$ @akonar, No problem. Welcome to the site, take the tour to familiarize yourself with it. If this solved your problem, you could mark the post as solved. :-) $\endgroup$
    – Jason B.
    Commented Feb 25, 2016 at 14:33

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