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Matlab Types - Cell

Matlab TypesCompleted

Cell

In MATLAB, cell and structure are heterogeneous containers: special arrays that, unlike a regular array, can hold elements of different types.

  • A cell array directly extends the regular array — each element (called a cell) may be of a different data type
    • A single-element cell is therefore not very meaningful; “cell array” by default refers to one with multiple elements
    • A cell may itself be a cell array, forming a nested cell array
  • Example: |200
  • Curly braces {} are the cell delimiter

Properties and Display

  • iscell
  • Display
    • celldisp prints the contents of every cell of a cell array
    • cellplot shows the structural diagram of a cell array

Creation

  • Assignment statements

    1. C(ind) = {x}
    2. C{ind} = x
    • ind is an ordinary array index
    • These also serve to expand a cell array

  • Function cell(<[sz1,...,szn]>)

    • Returns an sz1-by-…-by-szn cell array, with every cell empty ([])
    • With a single argument sz1, returns an sz1-by-sz1 square cell array

  • These methods always produce a “rectangular” cell array; unassigned cells default to empty [].

Example:

>> A = cell(2,3)
A =
  2x3 cell array
    {0x0 double}    {0x0 double}    {0x0 double}
    {0x0 double}    {0x0 double}    {0x0 double}
>> A{1,1} = 'hello'
A =
  2x3 cell array
    {'hello'   }    {0x0 double}    {0x0 double}
    {0x0 double}    {0x0 double}    {0x0 double}
>> A(2,3) = {123} 
A =
  2x3 cell array
    {'hello'   }    {0x0 double}    {0x0 double}
    {0x0 double}    {0x0 double}    {[     123]}
>> A{3,3} = [1;2]
A =
  3x3 cell array
    {'hello'   }    {0x0 double}    {0x0 double}
    {0x0 double}    {0x0 double}    {[     123]}
    {0x0 double}    {0x0 double}    {2x1 double}

Access and Removal

A cell array is accessed via Matlab Array - Indexing; the only twist is that wrapping the index in parentheses () returns a cell sub-array (still of class cell), whereas wrapping the index in curly braces {} returns the contents themselves.

  • This is also why cell-array assignment has two forms.

Example:

>> A{2,3}
ans =
   123
>> A(2,3)
ans =
  1x1 cell array
    {[123]}

You can also delete or slice from a cell array with indexing:

  • A{ind} = [] clears the element at ind (assigns it the empty value)
  • A(ind) = [] removes a slice from A
    • To keep A rectangular, only one component of ind may differ from :
    • In other words, you can only remove whole rows or columns

Nesting

A cell of a cell array can itself be a cell array, producing a nested cell array. Construction and access follow the rules of an ordinary array.

>> A{2,2} = {1, 2;'hello', cell(2)}
A =
  2x2 cell array
    {0x0 double}    {0x0 double}
    {0x0 double}    {2x2 cell  }
>> A{2,2}(2,1)
ans =
  1x1 cell array
    {'hello'}
>> A{2,2}{2,2}(2) = {'sub'}
A =
  2x2 cell array
    {0x0 double}    {0x0 double}
    {0x0 double}    {2x2 cell  }
>> A{2,2}{2,2}{2}           
ans =
    'sub'
  • In a nested cell array, the intermediate indices typically use curly braces {}.

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