Replace elements in matrix based on indices stored in another matrix

3 次查看（过去 30 天）
LM_BU
LM_BU 2018-7-31
评论： Star Strider 2018-7-31
I will probably be unable to articulate the problem well.
There are three variables, indicating indices:
a = [3:10, 17:21, 28]; b = [11:13, 22:24, 29:30]; c = [14:16, 25:27];
These are all indices in a categorical fashion (each variable is a category). Now, I want to create a variable to feed into a RepeatedMeasuresModel; hence, I will need some sort of dummy coding. To automate this, I want to have a matrix whose elements are 1, 2 or 3 (thereby representing a/b/c), based on the indices from the said variables.
E.g. conditions = [1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 1, 1, ...., 2, 2]; %n = 30. How do I output this? I have tried logical indexing, but it fails, because the matrices are not the same size. E.g. conditions = 1:30; conditions(conditions==a) = 1;
A side question, how would I, instead of say using 1/2/3 integers, use char arrays instead? For instance, instead of 1, we want to place the "value" 'Category1', 2 = 'Category 2', etc.
Thanks for your support.

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2018-7-31
I am not exactly certain what you want.
Try this:
a = [3:10, 17:21, 28];
b = [11:13, 22:24, 29:30];
c = [14:16, 25:27];
conditions = zeros(1,30); % Preallocate
conditions(a) = 1;
conditions(b) = 2;
conditions(c) = 3
cats = cell(1,30); % Preallocate
cats(a) = {'Category1'};
cats(b) = {'Category2'};
cats(c) = {'Category3'}
conditions =
' 0 0 1 1 1 1 1 1 1 1 2 2 2 3 3 3 1 1 1 1 1 2 2 2 3 3 3 1 2 2 '
cats =
' Category1 Category1 Category1 Category1 Category1 Category1 Category1 Category1 Category2 Category2 Category2 Category3 Category3 Category3 Category1 Category1 Category1 Category1 Category1 Category2 Category2 Category2 Category3 Category3 Category3 Category1 Category2 Category2 '

更多回答（1 个）

Stephen23
Stephen23 2018-7-31
编辑：Stephen23 2018-7-31
Just use indexing, which is simple and very efficient:
>> C{1} = [3:10, 17:21, 28];
>> C{2} = [11:13, 22:24, 29:30];
>> C{3} = [14:16, 25:27];
>> cond = [1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 1, 1, 2, 2];
>> Z = C(cond)
  1 个评论
LM_BU
LM_BU 2018-7-31
Hi Steve,
Thank you, but this does not answer my question. C{1..3} hold indices. I want to create another variable (your "cond"), but without manually adding those values myself. The result should be something like cond = 3:30; cond(a) = 1; cond(b) = 2; cond(c) = 3; Basically, I need to "flag" a matrix of 30 columns what category each column represents, based on the indices in a, b, and c.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by