Fastest alternatives to flattening a non-uniform nested array with regex?


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# 1  
Fastest alternatives to flattening a non-uniform nested array with regex?

Hello,

I'm looking at simplfying a function that flattens an array, it uses recursion and filters objects by type but this seems to be a waste of resources to me at least, using conditionals like this seems like a bad idea.

The array can be a generic type, int, string, float but not some container with mixed types.

For example
Code:
myArray:[Int]=[[-2, 5], 16, [-6, [9, [-3, [3, 1, 0]]]]]

Code:
for element in myArray 
{
  flatArray.append(element as! Int)
} else if element is [Any] { 
  recursionResult = flattenArray(nestedArray: element as! [Any])
  for num in recursionResult {
    flattenArray.append(num)
   }
}

The final result for this would be
Code:
[-2,5,16,-6,9,-3,3,1,0]

So I came up with this simple regex

Code:
/\-?[0-9]/g

Is there a more efficient way?
Thanks.
# 2  
My opinion:

As a general solution that seems fine. I have not validated it. Are you encountering performance problems?
BTW the PCRE regex is very well optimized and is regex-directed, so you can switch to that on most linux boxes with no problems.

Not that the 'old' regex code is not optimized.

I like your solution, but I wonder about what you are seeing as a problem. Selecting a regex engine is a lot messier than in long ago times:
Comparison of regular expression engines - Wikipedia

However PCRE is considered to be as good as it gets. You could write a simple single purpose C program....

Last edited by jim mcnamara; 03-30-2018 at 10:58 AM..
This User Gave Thanks to jim mcnamara For This Post:
# 3  
Quote:
Originally Posted by jim mcnamara
My opinion:

As a general solution that seems fine. I have not validated it. Are you encountering performance problems?

You could write a simple single purpose C program....
Thanks for the comments.

Yes, I tried some long, really off-the-wall, random arrays that would be equivalent to a messy json structure and the simple regex easily beat the recursion.

Good idea about C code, what do you think about the performance gain and memory utilization of using a threaded version? versus openmp/mpi? or versus GPU, if the incoming array is a continuous stream from a web socket? or similar.

For single precision, Int16 or UInt16, it seems like GPU would crush this problem but I'm unsure of the overhead required for the memory allocation.

Last edited by f77hack; 03-31-2018 at 06:52 PM.. Reason: add memory stuff
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