Question

>> x = {  {'a',[1],[2]};  {'b',[3],[4]}  }
x =    
    {1x3 cell}
    {1x3 cell}

>> A1 = x(1)    
A1 =     
    {1x3 cell}

>> A2 = x{1}   
A2 =    
    'a'    [1]    [2]

请注意，A1和A2的显示方式不同。

A1和A2报告为同一类和维度：

>> info = @(x){class(x),size(x)};
>> info(A1)     
ans =    
    'cell'    [1x2 double]

>> info(A2)     
ans =     
    'cell'    [1x2 double]

然而他们并不被认为是平等的：

>> isequal( A1, A2 )    
ans =    
     0

但是，A1{:} 被视为等于A2：

>> isequal( A1{:}, A2 )    
ans =    
     1

有人能解释一下这里发生了什么吗？

Answer 1

()用于函数输入和索引数组; []用于表示数组; {}用于索引单元格。

A = [2 1]; % Creates and array A with elements 2 and 1
A(2) =2; % Sets the second element of A to 2
B = cell(1,2); % creates a cell array
B{2} = A; % Stores A in the second cell of B

总之：x(1)选择数组x的第一个元素或评估x处的函数1; x[1]不可能，因为方括号不能用于索引内容; x{1}将选择单元格数组x中的第一个单元格。

关于你的具体问题：

A1 = x(1); % makes a copy of the element on index one, being a 1x3 cell
A2 = x{1}; % stores the content of the cell at element 1 in A2

最后A1{:}从单元格中获取单元格的内容，准备作为单独的变量存储，因此它等于A2，它已经包含该内容。（A1{:}是comma separated list，感谢rayryeng指出这一点。）

Answer 2

data {1}用于访问单元格的内容 data（1）用于创建具有第一个数据条目副本的单元格。这与：

相同

rake db:migrate

在您的示例中，A1因此是包含单元格的单元格，而A2是具有三个条目的单元格

Answer 3

Your variable x is a cell containing 2 (sub)cells.

Curly brackes is used to get the content of a cell, thus,
```
A2 = x{1}
ans = 
   'a'    [1]    [2]
```
Which gives the same result as
```
A2 = {'a',[1],[2]}
```
Parentheses is used for indexing and therefore returns a subset of the (sub)cells
```
A1 = x(1)    
A1 =     
    {1x3 cell}
```
Which gives the same result as
```
A1 = { {'a',[1],[2]} }
```

Your anonymous info function returns a cell (needs to as the content is of mixed types). The result

'cell'    [1x2 double]

tells that both A1 and A2 is cells which is true, not considering the fact that A1 is a cell containing cells and A2 is a cell containing a char and 2 numbers.

The [1x2 double] simply tells that the answer from size is itself of size [1x2]. This is true as long as you don't use higher dimensions than 2.

If you dig deeper into your info answer you will see the real size:

A1info = info(A1);
A2info = info(A2);
A1info{2}
ans =
     1     1
A2info{2}
ans =
     1     3

The part of isequal( A1, A2 ) beeing false I think you understand by now.

Also, that isequal( A1{:}, A2) is true, since {:} "de-cell" A1 and pick out its content. In this case, you could have typed isequal( A1{1}, A2) as well

x（1）和x {1}之间的差异

3 个答案: