Add new "datetime" elements to an existing cell array (matrix)

Question

Sim 2022-10-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1833738-add-new-datetime-elements-to-an-existing-cell-array-matrix

评论： Star Strider 2022-10-24

What I have so far:

a = cell(3,3);
index = [1 1
         2 1
         3 3];
b = datetime({'00:01:35'
             '00:01:11'
             '00:04:21'});
idx = sub2ind(size(a),index(:,1),index(:,2))
idx = 3×1
     1
     2
     9
a(idx) = num2cell(b) 
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21]}

What I need / Desired output: add further elements to the cell array (matrix) "a".

% For example, add the new element "datetime({'00:01:01'})"
% to the cell "index = [3 3]", i.e. "idx = 9":
a =
  3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                    }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double                                    }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21], [24-Oct-2022 00:01:01]}

My attempt:

new_element = datetime({'00:01:01'});
a(9) = a + num2cell(new_element)
Operator '+' is not supported for operands of type 'cell'.

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Answer 1

Star Strider 2022-10-24

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1833738-add-new-datetime-elements-to-an-existing-cell-array-matrix#answer_1082083

在 MATLAB Online 中打开

I am not certain what a more universal end result would look liks, however this seems to work for this problem —

a = cell(3,3);
index = [1 1
         2 1
         3 3];
b = datetime({'00:01:35'
             '00:01:11'
             '00:04:21'});
idx = sub2ind(size(a),index(:,1),index(:,2))
idx = 3×1
     1
     2
     9
a(idx) = num2cell(b) 
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21]}
new_element = datetime({'00:01:01'})
new_element = datetime
   24-Oct-2022 00:01:01
a{9} = [a{9} new_element]                                                           % Concatenate
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                    }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double                                    }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:01]}

The operation is a simple concatenation, using the [] concatenation operators.

.

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Star Strider 2022-10-24

在 MATLAB Online 中打开

As always, my pleasure!

The second num2cell call is not necessary, since ‘new_element’ or ‘new_elements’ do not need to be cell arrays themselves. Also, in my tweak to your original code, the previous value stored in ‘a(9)’ is retrieved as ‘a{9}’ allowing the concatenation to proceed.

The previous concatenation approach works here as well —

a = cell(3,3);
index = [1 1
         2 1
         3 3];
b = datetime({'00:01:35'
             '00:01:11'
             '00:04:21'});
idx = sub2ind(size(a),index(:,1),index(:,2))
idx = 3×1
     1
     2
     9
a(idx) = num2cell(b) 
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21]}
new_elements = datetime({'00:01:01' ...
               '00:01:56'});
a{9} = [a{9} new_elements]                                                           % Concatenate
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                                            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double                                                            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:01    24-Oct-2022 00:01:56]}

Since I am not exactly certain where this is starting from, confirming this —

a = cell(3,3);
index = [1 1
         2 1
         3 3];
b = datetime({'00:01:35'
             '00:01:11'
             '00:04:21'});
idx = sub2ind(size(a),index(:,1),index(:,2))
idx = 3×1
     1
     2
     9
a(idx) = num2cell(b) 
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21]}
new_element = datetime({'00:01:01'})
new_element = datetime
   24-Oct-2022 00:01:01
a{9} = [a{9} new_element]                                                           % Concatenate
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                    }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double                                    }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:01]}
new_elements = datetime({'00:01:01' ...
               '00:01:56'});
a{9} = [a{9} new_elements]                                                          % Concatenate
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                                                                    }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double                                                                                    }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:01    24-Oct-2022 00:01:01    24-Oct-2022 00:01:56]}
view_a_9 = a(9)                                                                     % Confirm Result
view_a_9 = 1×1 cell array
    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:01    24-Oct-2022 00:01:01    24-Oct-2022 00:01:56]}

Repeated concatenations work as well, duplicating the original second datetime value, if desired.

.

Sim 2022-10-24

编辑：Sim 2022-10-24

在 MATLAB Online 中打开

Thanks a lot for your reply @Star Strider :-) Very kind!

However, I meant something slighlty different, i.e. to add two new elements at the same time into two different cells, and not into the same cell as you have shown (cell [3 3])....

I try to write down what I meant.... and sorry for not having explained clearly, my fault ! :-) ....and, please let me know if I need to create a new question in Matlab Ask...

% (1) create the cell array / matrix "a" 
a  = cell(3,3);
% (2) add the first elements to the cell array / matrix "a" 
index = [1 1
         2 1
         3 3];
b = datetime({'00:01:35'
             '00:01:11'
             '00:04:21'});
idx = sub2ind(size(a),index(:,1),index(:,2));
a(idx) = num2cell(b) 
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double            }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {0×0 double            }
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21]}

Here below I show what I need, but without the loop for (if possible)!

% (3) add two new elements: 
% - one new element inside the cell [2 3] 
% - one new element inside the cell [3 3]
index2 = [2 3
          3 3];
new_elements = datetime({'00:01:01'
                         '00:01:56'});
idx2 = sub2ind(size(a),index2(:,1),index2(:,2));
for i = 1 : size(idx2,1)
    a{idx2(i)} = [a{idx2(i)} new_elements(i)];
end
a,
a = 3×3 cell array
    {[24-Oct-2022 00:01:35]}    {0×0 double}    {0×0 double                                    }
    {[24-Oct-2022 00:01:11]}    {0×0 double}    {[24-Oct-2022 00:01:01                        ]}
    {0×0 double            }    {0×0 double}    {[24-Oct-2022 00:04:21    24-Oct-2022 00:01:56]}