joinRepeatingVariableFast ( variableName ; delimiter ; startIndex ; endIndex )
Join / concatenate a large repeating variable / array using a delimiter character
Average rating: 4.3 (29 votes) Log in to vote
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Sam Barnum - Show more from this author
360Works http://360works.com |
$$foo[2] = "BAR"
$$foo[3] = "BAZ"
joinRepeatingVariable("$$foo" ; ", " ; "1" ; "3")
Function definition: (Copy & paste into FileMaker's Edit Custom Function window)
Uses a recursive "divide and conquer" approach to concatenating a large array of values, yielding better performance than simply iterating over the array appending each item to a large string.
Unlike the version at http://www.briandunning.com/cf/1285, this focuses primarily on performance, and does not stop when it reaches the end of the array (all parameters are required).
There is a commented line which clears out the array contents as they are appended, saving memory at a small speed penalty.
The performance increase is achieved by avoiding creating/appending to very large strings. Instead, most of the concatenation operations happen on smaller strings, the smaller bits being built into larger strings at the end.
Benchmarks from a 10,000 repetition variable, each entry 100 characters long:
* Looping append Script, simple: 13,505ms
* joinRepeatingVariable Recursive Concatenation CF: 6,904ms
* joinRepeatingVariableFast CF with clearing array: 2,960ms
* joinRepeatingVariableFast CS without clearing array: 2,330ms
* Looping "divide and conquer" script: 1,930ms
For 20,000 repetitions:
* Looping append Script, simple: 79,026ms
* joinRepeatingVariable Recursive Concatenation CF: ? (too many recursions)
* joinRepeatingVariableFast CF with clearing array: 5,960ms
* joinRepeatingVariableFast CS without clearing array: 4,626ms
* Looping "divide and conquer" script: 3,979ms
For 40,000 repetitions
* Looping append Script, simple: 523,167ms
* joinRepeatingVariable Recursive Concatenation CF: ? (too many recursions)
* joinRepeatingVariableFast CF with clearing array: ? (too many recursions)
* joinRepeatingVariableFast CS without clearing array: (too many recursions)
* Looping "divide and conquer" script: 8,228ms
Note that these techniques fall apart once the arrays get too large, because of the stack limit. You would want to switch to a scripted approach to get around this, but use a similar mechanism where you concatenate the smallest strings first, then join them into larger and larger batches.
Comments
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Jeremy, NC Nov 19, 2012 |
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| Are you sure you're function is faster than the one you reference? Have you tested it and demonstrated it? Can you post a demo file somewhere? As far as I can tell, both algorithms have to perform the same O(N) string concatenations, and they even ultimately do those concatenations in the same order. Am I missing something? | ||
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Sam Barnum, 360Works Nov 20, 2012 |
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| Thanks Jeremy, I posted some benchmarks. During testing, I hit the "max stack" issue with FileMaker custom functions. I'd recommend writing a looping script if this becomes an issue. | ||
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Bruce Robertson Nov 21, 2012 |
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| Doesn't work as written (won't compile successfully in custom function editor). Example doesn't make sense. It calls a function JoinArray which is undefined. Example contains no index values. An example file would really be helpful because it is hard to tell what this is supposed to do. | ||
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Sam Barnum, 360Works Nov 21, 2012 |
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| Thanks Bruce, I had changed the name of the function, but forgot to update the recursive calls in the function itself | ||
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