How can I add n columns to a matrix?

26 次查看（过去 30 天）
Tom
Tom 2021-9-27
编辑： Stephen23 2021-9-28
Dear experts,
I have a Matrix X(4082x2). Now I want to add for example two columns to the matrix with every cell = 0.
That´s how I´ve done it so far:
amount_rows = numel(X(:,1));
randomdata = rand(amount_rows,1);
added_column = 0*randomdata;
X = [X added_column added_column];
Until now, that worked completely fine but my problem is that I now have a dataset where I need to add more than 100 columns. It would be pretty annoying to add those 100 times the added_column into the bracket (I hope you know what I mean). On top of that, I want the script to work for every dataset so that it automatically adds the "added_collumn" e.g. n-times. Somehow like that:
X = [X (added_column)*n]
(in the case described above n =2)
I know that this is not correct but I hope you get the idea.
Thanks in advance.
Kind regards, TG

请先登录，再回答此问题。

采纳的回答

Stephen23
Stephen23 2021-9-27
编辑：Stephen23 2021-9-28
A simpler, more versatile, and much more efficient approach is to use ZEROS:
R = size(X,1);
C = number_of_new_columns;
X = [X,zeros(R,C)];
Another simple approach is to use indexing (which implicitly fills the other new elements with zeros):
X(1, end+C) = 0 % Thank you Image Analyst
  2 个评论
Steven Lord
Steven Lord 2021-9-27
Ran in:
In the general case where you want to augment a matrix with copies of a vector (not necessarily the zero vector) you can use repmat.
A = magic(3)
A = 3×3
8 1 6 3 5 7 4 9 2
v = [42; -99; NaN]
v = 3×1
42 -99 NaN
B = [A, repmat(v, 1, 5)]
B = 3×8
8 1 6 42 42 42 42 42 3 5 7 -99 -99 -99 -99 -99 4 9 2 NaN NaN NaN NaN NaN
Or if you need to augment with a series of vectors that can be created by arithmetic operations you can use implicit expansion.
c = [1; 2; 3]
c = 3×1
1 2 3
d = 1:5
d = 1×5
1 2 3 4 5
E = [A, v, c+d] % c+d makes a 3-by-5 matrix
E = 3×9
8 1 6 42 2 3 4 5 6 3 5 7 -99 3 4 5 6 7 4 9 2 NaN 4 5 6 7 8

请先登录，再进行评论。

更多回答（0 个）

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

R2019b

Community Treasure Hunt

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

Start Hunting!

Translated by