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Re: Array vs. Hash for sparsely integer-indexed databy BrowserUk (Patriarch) |
on Jan 25, 2013 at 19:02 UTC ( [id://1015391]=note: print w/replies, xml ) | Need Help?? |
1. What (if any) storage inefficiency (relative to hashes) is created in perl when using arrays for sparsely indexed data? It all depends on 'how sparse'":
The hash size remains static for a given number of entries, regardless of how sparse they are. At 1 in 2, the array uses a little over half the space of the hash; but by 1 in 20, almost 3 times as much and by 1 in 50 nearly 10 times as much. And remember, if your integer range starts at 1 billion; the array would require ~12GB (of basically wasted space), to hold the lowest value. Whilst you could wrap that over in an api to subtract 1 billion from each index, the additional subroutine call overhead would completely negate the array's lookup speed advantage; and then some. 2. What (if any) lookup inefficiency (relative to arrays) is created in perl when using hashes for positive integer indexed keys? Test:
The array takes 0.4 seconds to do 2 million lookups of which 5% are found and 95% not. The hash takes 1.02 seconds to do the same lookups. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
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