I'm with Raul on this. A hashtable is a fine idea when memory is fast,
but if the hashtable greatly exceeds D3$ every hash lookup will be a
page miss which is hideous. A merge sort would look pretty good then.
Henry Rich
On 4/9/2022 3:23 PM, Elijah Stone wrote:
If ~.!.1 is used, then how would we denote a -. operating on sorted
arguments?
I build the hash table concurrently, using a multiprocessor; this
means the elements are processed out of order. Two ways of
proceeding, not yet sure which is better. The first is for each
thread to accumulate the unique values it finds to a temporary buffer;
once the hash table is completely built, the threads negotiate and
then copy their buffers into the result. The second is to logically
divide the hash table into fixed-size chunks of buckets, and to track,
for each chunk, how many of its buckets are occupied; once the hash
table is completely built, associate each chunk of the hash table with
a (non fixed-size) section of the result, and copy the elements out.
The former method does work concurrently with building the hash table,
which alleviates contention, but the latter method uses less space.
On Sat, 9 Apr 2022, Henry Rich wrote:
I would favor ~.!.1. No mnemonic value, but less likely to be
forgotten.
What is your fast algorithm?
Henry Rich
On 4/9/2022 4:03 AM, Elijah Stone wrote:
Suppose that ~. (and perhaps some relatives) can be implemented much
more efficiently if no guarantee is made about the order of the
result. Is it too much of an abuse of notation to use ({~?~@#)@~.
as a special combination to invoke such an algorithm? If so, what
would be better?
Most special combinations would not incur a performance penalty vs
an alternate expression of the same semantics on an implementation
which did not recognise special combinations. But I cannot think of
any way of expressing ambivalence regarding the order of a result
other than shuffling it.
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