valueDiff for arrays?

[Mark Waddingham]

On 2018-08-08 00:20, Bob Sneidar via use-livecode wrote:
> I do stand corrected however, as I got the dgdata of a grid with 6
> records, in the order they were added to the sql database, and then
> queried for. The keys are NOT in numerical order:
> 
> 5
> 6
> 1
> 2
> 3
> 4

The keys function does the minimal work necessary to return its result.

An array in LiveCode is a sequence of slots, each one which can hold a 
value (pre-7 they used to be chained hash-tables - but 7+ they changed 
to linear hash-tables).

The hash of the key is used to determine which slot its value goes in - 
if that slot is full it goes in the next available one.

The keys function iterates through the sequence of slots from 1 up to 
the capacity of the array (which is not the same as the number of 
elements - there's always head-room in the slot array), accumulating the 
keys which are present as it goes - any empty slots are skipped.

Therefore the ordering of the keys is determined by the numerical order 
of the hash of the keys themselves which holds scant relationship to the 
content of the keys - beyond that determined by the hash function - i.e. 
the hash function is designed to distribute keys arbitrarily, but 
uniformly across the sequence of slots.

Warmest Regards,

Mark.

-- 
Mark Waddingham ~ mark at livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps