I wonder if addTo() [1] would work. Alternatively, suppose you add vector2's elements to vector1. You could iterateNonZero [2] through vector2's elements, get the corresponding element in vector1 (with the same index), if it's zero, set its value to the one in vector2, otherwise... do whatever you want in case the vectors have different values for the same index (pick one version, add...).
[1] http://people.apache.org/~isabel/mahout_site/mahout-matrix/apidocs/org/apache/mahout/matrix/SparseVector.html#addTo(org.apache.mahout.matrix.Vector) [2] http://people.apache.org/~isabel/mahout_site/mahout-matrix/apidocs/org/apache/mahout/matrix/SparseVector.html#iterateNonZero() On Fri, Nov 30, 2012 at 12:55 AM, Stefan Kreuzer <[email protected]> wrote: > The vectors don't have the same cardinality, so vector1.plus(vector2) does > not work. > Is there a way to resize a given vector? Sorry I am a complette Mahout-noob. > > > > -----Ursprüngliche Mitteilung----- > Von: Ted Dunning <[email protected]> > An: user <[email protected]> > Verschickt: Do, 29 Nov 2012 11:45 pm > Betreff: Re: How to concatenate Vectors? > > > The most efficient way is probably to just add them. > > You can also use assign with a max function. Or you can write a special > function if you want the left vector or the right one to have preference. > > Vector a, b; > // method 1 > a.plus(b); > // method 2 > a.assign(b, Functions.MAX); > // method 3 > a.assign(b, new DoubleDoubleFunction() { > @Override > public double apply(double arg1, double arg2) { > return arg1 > 0 ? arg1 : arg2; > } > }); > > The assignment approaches have the problem that they not operate in a > sparse fashion except for a few known functions. It would be very easy to > extend the DoubleDoubleFunction so that there is a > isSparseFriendly() method or to introduce a new > SparseFriendlyDoubleDoubleFunction class to determine whether it would be > safe to do the iteration in a sparse fashion. The last example would > become: > > a.assign(b, new SparseFriendlyDoubleDoubleFunction() { > @Override > public double apply(double arg1, double arg2) { > return arg2 != 0 ? arg2 : arg1; > } > }); > > MAX is not a sparse friendly function, of course since max(x,0) != 0 in > general. > > On Thu, Nov 29, 2012 at 2:24 PM, Stefan Kreuzer <[email protected]>wrote: > >> Hello, >> >> I dont understand what is the best way to concatenate (or merge) two >> sparse vectors. >> I.e. given two sparse vectors >> {8:0.027,38:0.037,67:0.027} >> and >> {86:0.032,87:01042} >> I need to build a new vector that contains all the values of the two: >> {8:0.027,38:0.037,67:0.027,86:0.032,87:01042} >> >> What is the best / most efficient way to achieve this in Mahout? >> >> Best Regards >> Stefan >> > > > work
