(PS I don't think that link from Ted is publicly visible but try
http://www.slideshare.net/tdunning )
Maybe I'm walking into half of a another conversation but what's the
question or goal here?
I don't think the matrix product contains quite what you're saying.
For example U1 records only 2 ratings but has some "enthusiasm" on 3
separate days in the matrix product. The product is mashing together
itemday associations from all users and applying them to each user.
Conceptually useritemday is the 3dimensional matrix that it sounds
like, if you want to distinguish associations from different users to
different items on different days.
On Tue, Nov 23, 2010 at 7:24 AM, Lance Norskog <goksron@gmail.com> wrote:
> The GroupLens dataset has User, Item, Rating and Timestamp.
> We will use the rating of 15 asis, but will reduce the timestamp
> field to day of the week.
> The lack of a rating defaults two 3 (neutral). There are 5 ratings
> total in the sample:
>
> U1, I1, 2, ?
> U1, I3, 4, ?
> U2, I1, 4, ?
> U2, I2, 5, T
> U2, I3, 3, ?
>
> (We'll get to the question marks later.)
> Now, make two matrices, User v.s. Item and Item v.s. Day of the Week.
> User v.s. Item contains ratings, and Item v.s. Day of the Week
> contains the number of rating records for that item on that day of the
> week: ratings only cover Sunday, Monday and Tuesday.
>
> Formatting tables in kerned fonts just plain doesn't work, thus the
> alternate format.
>
> 2 Users v.s. 3 Items:
> I1,I2,I3
> {
> U1 {2,3,4}
> U2 {4,5,3}
> }
>
> 3 Items v.s. 7 Days of the Week
> S,M,T,W,T,F,S
> {
> I1 {1,0,1,0,0,0,0}
> I2 {0,0,1,0,0,0,0}
> I3 {0,1,1,0,0,0,0}
> }
>
> Now, multiply these two matrices. The product is 2 Users v.s. 7 Days
> of the Week:
> S,M,T,W,T,F,S
> {
> U1 {2,4,9,0,0,0,0}
> U2 {4,3,12,0,0,0,0}
> }
>
> This matrix carries the total amount of enthusiasm for each user on
> each day. To get the average enthusiasm of each user, divide each row
> by the total number of ratings per day:
> S,M,T,W,T,F,S
> {
> U1 {2,4,3,0,0,0,0}
> U2 {4,3,4,0,0,0,0}
> }
>
> Did I get this right, Ted?
>
> BTW, where are your slides for this topic? I've seen them a couple of
> times in presentations (live and on Fora.tv), but can't find them.
>
> 
> Lance Norskog
> lance.norskog@gmail.com
>
