On Mar 5, 2009, at 4:59 PM, Wout Mertens wrote:
Actually, I just did some tests around this, and it turns out that
if you always query with group=true, CouchDB never runs the final
rereduce!
So based on this, I created this reduce function for reducing a maps
emit(key,value) to unique values per key:
function(k,v,r) {
function unique_inplace(an_array) {
var first = 0;
var last = an_array.length;
// Find first non-unique pair
for(var firstb; (firstb = first) < last && ++first < last; ) {
if(an_array[firstb] == an_array[first]) {
// Start copying, skipping uniques
for(; ++first < last; ) {
if (!(an_array[firstb] ==
an_array[first])) {
an_array[++firstb] =
an_array[first];
}
}
// firstb is at the last element of the new
array
++firstb;
an_array.length = firstb;
return;
}
}
}
if(r) {
var arr=[];
for (var i=0; i<v.length; i++) {
arr=arr.concat(v[i]);
}
arr=arr.sort();
unique_inplace(arr);
return(arr);
} else {
var arr=v.sort();
unique_inplace(arr);
return(arr);
}
}
It's not optimal yet, ideally the if(r) section should use an n-way
mergesort+uniq since it receives sorted arrays as values. But this
also works :).
Thoughts?
Wout.
