counting runs

Dick Kriesel dick.kriesel at
Mon Oct 31 21:09:12 EST 2005

On 10/31/05 4:22 PM, "Jason Tangen" <j.tangen at> wrote:

> Hello,
> I'm trying to solve a seemingly simple problem and I could use some
> help. A coin flip will come out "Heads" or "Tails" and will produce,
> for example, the following series for 20 flips:
> T,T,H,T,T,H,H,H,T,T,H,T,H,H,H,T,H,T,H,T
> I need to count up the number events for a particular run.  For example,
> Heads x 3 = 2
> Heads x 2 = 0
> Heads x 1 = 4
> Tails x 1 = 4
> Tails x 2 = 3
> Tails x 3 = 0
> I need to account for runs up to 60 (rather than 3 above) for
> hundreds of flips (rather than 20 above).
> I've been using a very clumsy multiple if-then solution to date, but
> this quickly becomes difficult with many runs.
> Can someone point me in the right direction?
> Cheers,
> Jason

Here's yet another solution.  At the core, it uses an array like Alex's
solution, but with slightly fewer instructions.  So all it really adds to
suggestions already posted is a technique for reporting results as the
original example suggests: runs of heads first sorted by descending run
length, followed by runs of tails sorted by ascending run length, with no
run lengths missing.

-- Dick

post script:

local sArray,sChar,sCount,sMax

on mouseUp
  ask "enter a comma-delimited sequence of H's and T's" \
      with "T,T,H,T,T,H,H,H,T,T,H,T,H,H,H,T,H,T,H,T"
  recordFlips it
end mouseUp

on recordFlips pSequence
  put "" into sArray
  put char 1 of pSequence into sChar
  put 0 into sCount
  put 0 into sMax
  repeat for each item tChar in pSequence
    recordFlip tChar
  end repeat
  add 1 to sArray[sChar,sCount]
end recordFlips

on recordFlip pChar
  if pChar = sChar then
    add 1 to sCount
    if sCount > sMax then
      put sCount into sMax
    end if
    add 1 to sArray[sChar,sCount]
    put pChar into sChar
    put 1 into sCount
  end if
end recordFlip

on putResults
  -- note: fill in any missing runs
  put the keys of sArray into tKeys
  repeat with i = 1 to sMax
    if sArray["H",i] is empty then put 0 into sArray["H",i]
    if sArray["T",i] is empty then put 0 into sArray["T",i]
  end repeat
  -- note: sort runs of heads descending, then runs of tails ascending
  put the keys of sArray into tKeys
  sort tKeys numeric descending by sortKey(each)
  -- note: put the results
  put ""
  repeat for each line tKey in tKeys
    put item 1 of tKey && "x" && item 2 of tKey & ":" && sArray[tKey] & cr
after msg
  end repeat
end putResults

function sortKey pKey
  if item 1 of pKey is "H" then put item 2 of pKey into tSortKey
  else put 0 - item 2 of pKey into tSortKey
  return tSortKey
end sortKey

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