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  ClearAll["`*"]
    
    deck = Sort[
      Join[Range[102, 114], Range[202, 214], Range[302, 314], Range[402, 414]]]
    Length[deck]
    
    holeCards = 
     Sort[RandomChoice[deck, 2]] (*selects two random cards from our deck*)
    
    communityDeck = 
     DeleteCases[deck, 
      Alternatives @@ 
       holeCards] (*creates a new deck and removes the holeCards*)
    Length[communityDeck]
    
    orderQ[card1_, card2_] := card1 < card2;
    valueSort[hand_] := Sort[hand, orderQ]
    
    cohands = Subsets[communityDeck, {5}] // Map[Join[#, holeCards] &]
    sortedHands = valueSort /@ cohands
    
    (* A pair *)
  
    pair0Q[{___, x_, x_, ___}] := True;(* a pair*)
    pair0Q[{___, x_, x_, x_, ___}] := False;
    pair0Q[{___, x_, x_, ___, y_, y_, ___} /; x != y] := False;
    pair0Q[{___}] := False;
    pairQ[hand_] := pair0Q[Sort[Mod[hand, 100]]]
    
    Count[sortedHands, _ ?(pairQ)]/Length[sortedHands]
    
    (* Two Pairs *)
    
    twoPairQ[{___, x_, x_, ___}] := False;
    twoPairQ[{___, x_, x_, x_, ___}] := False;
    twoPairQ[{___, x_, x_, ___, y_, y_, ___} /; x != y] := True;(*two pairs*)
    twoPairQ[_] := False;
    pair2Q[hand_] := twoPairQ[Sort[Mod[hand, 100]]]
    
    Count[sortedHands, _ ?(pair2Q)]/Length[sortedHands]
    
    (* Straight Flush *)
    
    straightFlusQ[h_] := 
     MatchQ[h - h[[1]], {0, 1, 2, 3, 4, _, _}] || 
      MatchQ[h - h[[2]], {_, 0, 1, 2, 3, 4, _}] || 
      MatchQ[h - h[[3]], {_, _, 0, 1, 2, 3, 4}]
    
    Count[sortedHands, _ ?(straightFlusQ)]/Length[sortedHands]
    
    (* Flush *)

This is my code. The deck has 52 cards in total. 2 cards are randomly chosen and act as holecards. the deck is returned in subsets of 5 for all possible combinations. the holecards are inserted back into each subset of 5 becoming subsets of 7. How do I write a code for the flush which is 5 random cards of the same suit?

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    $\begingroup$ RandomChoice[deck, 2]] can return duplicates, use RandomSample. Also this works sortedHands = Sort /@ cohands $\endgroup$
    – Rohit Namjoshi
    Sep 22, 2021 at 19:52
  • $\begingroup$ Suits are being encoded as the first digit, you can extract it e.g. IntegerDigits[310] // First gives 3, and count the number of occurrences. {102, 113, 203, 302, 305, 306, 412} // Map[IntegerDigits /* First] // Counts. $\endgroup$
    – Rohit Namjoshi
    Sep 22, 2021 at 20:06
  • $\begingroup$ How does your set-up which involves 5 of 7 cards differs from what is described at en.wikipedia.org/wiki/Poker_probability ? I assume that the 5-car flush is based on the optimal selection of 5 from 7 cards. $\endgroup$
    – JimB
    Sep 23, 2021 at 21:12
  • $\begingroup$ Your code seems to have the objective of finding the probability of a resulting poker resulting (a pair, straight flush, flush, etc.) given the two particular hole cards selected. Is that what you want? That's different from the probability of obtaining a flush with 7 cards. $\endgroup$
    – JimB
    Sep 24, 2021 at 3:18

1 Answer 1

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A faster option than the one in the comment

flushQ[hand_] := MatchQ[hand/100 // Floor, {___, x_, x_, x_, x_, x_, ___}]

Count[sortedHands, _?flushQ]/Length[sortedHands]
(* 20889/1059380 *)
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