add the value of column from text file to the value to matrix

i create a matrix having userid as a row and itemid as a column ,now i want to add the value of the third column ,in the index value of userid,itemid.Initially fill the matrix by zeros,but now want the value associate with it.

data=load('u.data');
uni_user=unique(data(:,1));
uni_item=unique(data(:,2));
rating_matrix=zeros(length(uni_user(:,1)),length(uni_item(:,1)));

example this is my dataset

196 242 3

186 302 3

22 377 1

196 51 2

now i want a matrix like

[Walter Roberson]

You need to add the 'stable' option to unique()

You will probably also want the third output of unique()

[RUCHI CHOUDHARY]

but how can i acess the third column value and store them to matrix ,to its related index,that value 3 is stored at (196,242).

[Walter Roberson]

The third output of unique() is a relative index.

sparse(user_index_from_unique, item_index_from_unique, data(:,3))

[RUCHI CHOUDHARY]

i think my question in not clear.matrix is not square matrix so how can we sparse().In actual data file i have 973 unique user and 1683 unique item, so 973*1683 size of matrix is create in which total 10000 rows in column 3 of file is present ,which i want to store in matrix at the index loaction of user and item.possible that for loop is requred to store that data.but i don't know how to use that.

Thank you

[Walter Roberson]

sparse() does not require square matrices.

>> full(sparse(1:5,[1 2 3 1 2],1))
ans =
     1     0     0
     0     1     0
     0     0     1
     1     0     0
     0     1     0

Answer 1

[Walter Roberson]

data = load('u.data');
[uni_user, ~, uni_user_idx] = unique(data(:,1));
[uni_item, ~, uni_item_idx] = unique(data(:,2));
rating = data(:,3);

rating_matrix = sparse(uni_user_idx, uni_item_idx, rating);

This will have about 0.6% occupancy and so is well suited for a sparse matrix, but if you have particular reason, you can full() to turn it into a 12 megabyte rectangular array.