MATLAB: Add the value of column from text file to the value to matrix

columnmatrix

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

Best Answer

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.

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MATLAB: Reading and separating data

Basically, you have two issues here: 1) importing the data into matlab, 2) rearranging it so that it's indexed by item number instead of time.

For 1), it would be much easier to work from the original text file, but since you've not posted that, I'll work with the excel file. Note that an excel file is not a text file and cannot be manipulated as such. The code for reading a text file or an excel file would be completely different. So for now, I'll simply do:

[numbers, text] = xlsread('value[1].xls')
itemtimes = datenum(regexp(text(1:5:end), '(?<=Time ).*', 'match', 'once'), 'yyyy/mm/dd HH:MM:SS.FFF');

Now for 2), the simplest thing is to iterate over the itemtimes and extract item numbers, values, and increase into a new container indexed by item number. The best containers would be either structures or maps. I'll use a map:

itemmap = containers.Map('KeyType', 'double', 'ValueType', 'any');
for row = 1:numel(itemtimes)
    itemtime = itemtimes(row);
    itemids = numbers((row-1)*5+2, :);
    itemvalues = numbers((row-1)*5+3, :);
    itemincreases = numbers((row-1)*5+4, :);
    for col = 1:sum(~isnan(itemids))
       newrow = [itemtimes(row) itemvalues(col) itemincreases(col)];
       if isKey(itemmap, itemids(col))
          itemmap(itemids(col)) = [itemmap(itemids(col)); newrow];
       else
          itemmap(itemids(col)) = newrow;
       end
    end
end

Each value in the map is an Nx3 matrix, where the first column is the time, the second column is the value and the third is the increase. So for example, for plotting Value vs Time for item 11:

m = itemmap(11);
plot(m(:, 1), m(:, 2));
datetick(gca);

MATLAB: Extract identical values from a data set

The error Error using == Matrix dimensions must agree is raised because u(n>1) contains a subset of the elements of R and so these two vectors are of different dimension and when comparing the two with ==, it will fail because of this difference in dimension.

Since R is a distance value (from http://www.mathworks.com/help/matlab/ref/cart2pol.html) then you may have different values that could be considered the same but due to the double data type used you will not be able to group the two as identical using (say) unique. For example,

 1.1234567
 1.1234568

Should the above two numbers be considered the same? If so, then you can group like values in R that should be considered identical, given a tolerance.

We sort the data first, and then do the grouping. If we assume that each of the TH, R, and Z are vectors (as opposed to matrices) we can do

 data = [R Z TH];

Now sort the data as

 sortedData = sortrows(data,1);

In the above, we just sort on the first column of data which corresponds to our R data. We can then iterate over the data and find all those elements that should be considered part of the same group given a tolerance

 myTol       = 0.00001; % use myTol to determine if 2 values should be consided same
 grpStartIdx = 1;       % start index of group
 grpStopIdx  = 1;       % stop index of group
 groupedData = {};      % a cell array for the grouped data
 atGroupIdx  = 0;
 % iterate over each row of sortedData starting at second element
 for k=2:size(sortedData,1)
   % compare the first element with the previous
   if abs(sortedData(k,1)-sortedData(k-1,1)) < myTol
      % the two consecutive elements are considered to be identical
      % so must be part of same group
      grpStopIdx = k;
   else
      % the two consecutive elements are not identical since their difference
      % is greater than myTol so we have come to a new group
      grpStopIdx = k-1;
      % copy all data (R,Z,TH) as a group to the cell array
      atGroupIdx = atGroupIdx + 1;
      groupedData{atGroupIdx} = sortedData(grpStartIdx:grpStopIdx,:);
      % update next group indices
      grpStartIdx = k;
      grpStopIdx  = k;
   end
 end
 % copy the last group
 atGroupIdx = atGroupIdx + 1;
 groupedData{atGroupIdx} = sortedData(grpStartIdx:grpStopIdx,:);

The above may contain a little more code that you wish (and not as neat as using the built-in MATLAB functions), but each group of near-identical R data (as determined by myTol) are combined together in the cell array groupedData for further processing.

Best Answer

Related Solutions

MATLAB: Reading and separating data

MATLAB: Extract identical values from a data set

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