How can i perform lexicographic sorting on a cell ?

Hi,

As a part of may work i first divide an image into number of overlapping blocks and dct for each blocks are calculated.Then from each block 4 features are extracted and they are saved into a cell.Then that cell contains 4 columns and rows equal to number ob blocks.Then i want to perform lexicographic sorting on this feature vector cell,how can i perform that?

[Arun Mathew Iype]

Does the cell array contain strings or numbers

Answer 1

[Arun Mathew Iype]

Check the sortrows function for sorting cell arrays which gives a lexicographical/dictionary sort. You can find examples and description in the below link.

http://www.mathworks.com/help/releases/R2014a/matlab/ref/sortrows.html

Example :

    %Create a 6-by-2 cell array of strings.
    A = {'Germany' 'Lukas'; 'USA' 'William'; 'USA' 'Andrew'; ...
    'Germany' 'Andreas'; 'USA' 'Olivia'; 'Germany' 'Julia'} 

    %Sort the rows of A.
    B = sortrows(A)

Output:

A = 

      'Germany'    'Lukas'  
      'USA'        'William'
      'USA'        'Andrew' 
      'Germany'    'Andreas'
      'USA'        'Olivia' 
      'Germany'    'Julia'  

B = 

      'Germany'    'Andreas'
      'Germany'    'Julia'  
      'Germany'    'Lukas'  
      'USA'        'Andrew' 
      'USA'        'Olivia' 
      'USA'        'William'

In case you want to do a lexicographic sorting of numbers, you can use this workaround wherein you first change the numbers to string Example :

    orig_cell_array ={7 4; 6 1; 20 2; 5 3}

    % Convert to a string array
    str_array = cellfun(@num2str,orig_cell_array,'UniformOutput',false)

    % Do lexicographical sorting
    sort_str_array = sortrows(str_array)

    % Convert back to numbers
    new_cell_array = cellfun(@str2num, sort_str_array,'UniformOutput',false)

Output :

orig_cell_array = 

      [ 7]    [4]
      [ 6]    [1]
      [20]    [2]
      [ 5]    [3]

str_array = 

      '7'     '4'
      '6'     '1'
      '20'    '2'
      '5'     '3'

sort_str_array = 

      '20'    '2'
      '5'     '3'
      '6'     '1'
      '7'     '4'

new_cell_array = 

      [20]    [2]
      [ 5]    [3]
      [ 6]    [1]
      [ 7]    [4]