transform an empty matrix '0x0 double' into a matrix '0x2 double'

11 次查看（过去 30 天）
Alberto Acri
Alberto Acri 2023-7-20
评论： Bruno Luong 2023-7-20
Hello! How can I transform an empty matrix '0x0 double' into a matrix '0x2 double' as in the figure?
For example in my case, I have a cell 'test_p'. Rows 3,4,5 (0x0 double) should become like rows 1 and 2 (0x2 double).
test_p = importdata("test_p.mat");
data_0x2_double = test_p{1, 1};
data_0x0_double = test_p{3, 1};

请先登录，再回答此问题。

采纳的回答

Bruno Luong
Bruno Luong 2023-7-20
编辑：Bruno Luong 2023-7-20
Ran in:
test_p = importdata("test_p.mat")
test_p = 5×1 cell array
{0×2 double} {0×2 double} {0×0 double} {0×0 double} {0×0 double}
ir = cellfun('size',test_p,1)==0 & cellfun('size',test_p,2)==0
ir = 5×1 logical array
0 0 1 1 1
test_p(ir) = {zeros(0,2)}
test_p = 5×1 cell array
{0×2 double} {0×2 double} {0×2 double} {0×2 double} {0×2 double}

更多回答（2 个）

Steven Lord
Steven Lord 2023-7-20
Ran in:
Since a 0-by-0 array and a 0-by-2 array have the same number of elements you can reshape one into the other.
A = zeros(0, 0)
A = []
B = reshape(A, [0 2])
B = 0×2 empty double matrix
C = reshape(B, 0, 0)
C = []
whos A B C
Name Size Bytes Class Attributes A 0x0 0 double B 0x2 0 double C 0x0 0 double
  3 个评论
显示 1更早的评论
Steven Lord
Steven Lord 2023-7-20
Ran in:
Your code below made an assumption about the user's data, one that's likely valid (and is valid WRT the original question) but in some cases may not be.
A = zeros(0, 0, 'single');
B = reshape(A, [0 2]);
C = zeros(0, 2);
whos A B C
Name Size Bytes Class Attributes A 0x0 0 single B 0x2 0 single C 0x2 0 double
B and C are different classes. You could modify the call that creates C to always create it 'like' A or with the same type as A, but reshape will not change the type and is shorter than either of the calls that create C1 or C2 below.
C1 = zeros(0, 2, 'like', A)
C1 = 0×2 empty single matrix
C2 = zeros(0, 2, class(A))
C2 = 0×2 empty single matrix

请先登录，再进行评论。

Adam Danz
Adam Danz 2023-7-20
编辑：Adam Danz 2023-7-20
Ran in:
To create an empty double with a specified size,
data_0x2_double = zeros(0,2)
data_0x2_double = 0×2 empty double matrix
Or,
data_0x2_double = double.empty(0,2)
data_0x2_double = 0×2 empty double matrix
See also Steve Lord's solution using reshape.

类别

在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

产品


版本

R2021b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by