array that grows in size over time

Question

vsee 2011-8-31

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14829-array-that-grows-in-size-over-time

Is there an option to declare an array in matlab that grows as a program runs (like a vector or a list in C++)? I am trying to read a .csv file with many data points and check for each data point to meet a certain requirement and if it does initialize it to another array and keep doing so until I reach the end of the file that I read using the csvread command?Thanks for any suggestions.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Fangjun Jiang 2011-8-31

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14829-array-that-grows-in-size-over-time#answer_20155

在 MATLAB Online 中打开

You don't need to declare it. MATLAB will automatically grow it. Although many will advise you not to do that because it slows things done, by in your case, it is really needed. For example,

>> clear a;
a=rand(3,1);
a(5)=20
a =
      0.1576
      0.9706
      0.9572
           0
     20.0000

2 个评论
显示无隐藏无

vsee 2011-8-31

Thanks. Does this mean that I have to declare a random array of certain size to start with?

Daniel Shub 2011-8-31

In general no, you do not have to declare anything to start with.

b(5) = 20

works just fine. That said, there can be a substantial performance hit (especially for versions before r2011a) of not initiating the size beforehand. If the maximum size is reasonable, you can trim afterwards:

c = nan(1000, 1); % Initialize to the maximum size

% Some code that loops

c = c(~isnan); % Trim the unused slots

请先登录，再进行评论。