Shuffling an array randomly

RE: Shuffling an array randomly

Mike Schmitt — Fri, 18 Dec 2020 15:30:40 GMT

Something like that would need to be built into the a!queryEntity function or one of its components - you could always file a feature request ticket with Appian Support, however I wouldn't expect it to be prioritized anytime soon without a strong use case on your end.

Out of boredom I went ahead and implemented a standalone function where you input the desired number of items and it returns a randomized list of integer indices 1...N, where we're guaranteed to have no duplicates or missing numbers. This integer array could then be used to index into any particular array in a randomized manner.

a!localVariables(
  
  local!targetSize: 25,
  
  local!dict: a!forEach(
    enumerate(local!targetSize),
    
    a!map(
      integer: fv!index,
      sort: rand()
    )
  ),
  
  local!sorted: todatasubset(
    local!dict,
    a!pagingInfo(
      startIndex: 1, batchSize: -1,
      sort: a!sortInfo(field: "sort", ascending: true())
    )
  ),
  
  local!sorted.data.integer
)

RE: Shuffling an array randomly

adityaamba — Fri, 18 Dec 2020 06:54:29 GMT

Thanks Mike,

This was a really innovative way to sort and shuffle a large array at low perofromance cost. But I feel that since we have the functionality of fetching randomly sorted records direct from SQL query in MySQL, Appian should incorporate a way to use that functionality as it will save a great coding time and performance load will be reduced.

RE: Shuffling an array randomly

Mike Schmitt — Thu, 17 Dec 2020 14:42:15 GMT

I like it - though it should be noted that this could occasionally (probably very rarely) return only 4 results if none of the 50 "coin flips" come up for one of the 5 numbers. I assume if you push the "random array length" value high enough you'll eventually get zero failures, though i'm not sure what that'll do to the efficiency of the rule.

I just tested and this happened 3 out of 10,000 times (though on some other runs of the same code it happened 0 times):

a!flatten(
  a!forEach(
    enumerate(10000), /* number of times to test */
  
    a!localVariables(
      local!length: 5,
      local!array: floor(rand(local!length*10) * local!length) + 1,
      if(
        length(union(local!array, local!array)) < local!length,
        "flag",
        {}
      )
    )
  )
)

RE: Shuffling an array randomly

normanc — Thu, 17 Dec 2020 14:12:15 GMT

This will give you the numbers 1..5 in a random order, which could be used as an index for the CDT array.

a!localVariables(
  local!array: floor(rand(50)*5)+1,
  union(local!array, local!array)
)

RE: Shuffling an array randomly

Mike Schmitt — Thu, 17 Dec 2020 14:10:17 GMT

There are various ways to do this, but anything you do you'll have to build yourself.

A quick-and-dirty way I just thought of:

use a!forEach to loop over the CDT array and use updateDictionary() to add a new ad-hoc property to each one, i.e. "order", set to the value of a rand() call. This will give a random decimal between 0 and 1 to all items; they should almost always be unique as far as I know.
Sort the array based on the "order" decimal (use the "toDataSubseet" trick to sort an array of dictionary based on the value of a property).