On 28 Jan 2010, at 03:09, Twan van Laarhoven wrote:
For example, in Map String Integer (sparse representation of
monomials) compute the minimum value of all associative pairs with
the same key (the gcd); if only one key is present, the absent
should be treated as having value 0. So
unionWith min xs ys
will not work, because unionWith will always apply the identity to
the remaining value when one key is missing, whereas it should be
sent to 0.
If missing keys represent 0, then wouldn't this work?
intersectionWith min xs ys
Yes, that works for the gcd function using min. Thank you - this
function is used a lot, so it is good to have it simple.
For the general problem, one still needs a better interface. For (-),
though missing keys represent 0, if the first is missing, the second
should be negated. And if both are present, one should filter out keys
with 0 value. Right now, this is a combination of negate, (+), and
filter (/= 0).
Hans
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
