How to convert each row of the matrix into a Character array, without using a for command?

Question

Jian Shi 2019-4-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/454163-how-to-convert-each-row-of-the-matrix-into-a-character-array-without-using-a-for-command

编辑： dpb 2019-4-6

Matlab code:

A=rand(1e3,2);%just an example
for i=1:size(A,1)
      B{i}=num2str(A(i,:));
end

Question: The cost time of the code is related to the size of A. How can I get the B without the For command and spend as less time as possible?

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

dpb 2019-4-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/454163-how-to-convert-each-row-of-the-matrix-into-a-character-array-without-using-a-for-command#answer_368860

在 MATLAB Online 中打开

Preallocate B may help just tad...

Alternatives to loop include

B=cellstr(num2str(A));

but what is end purpose for doing the conversion? Perhaps could avoid entirely??? The most time-saving optimization is the one that avoids doing the unneeded... :)

3 个评论
显示 1更早的评论隐藏 1更早的评论

dpb 2019-4-3

Show a small subset example with data set...I suspect you can use ismember or other logical addressing to solve the problem directly without the text step at all...but need an example to ensure we're on the same page.

Jian Shi 2019-4-6

编辑：dpb 2019-4-6

在 MATLAB Online 中打开

Ok, I have tried to use ismember but it is like other lookup functions that waste too much time on finding my expected value in Z at fixed point in (X,Y). For example

%every row of A is different, it can be considered as some point in R^2;
A=[1 3;2 4;2 7;6 19]; 
%every element of B is different, it can be considered as the value under an one-to-one mapping f(x,y) on A; 
AA=cellstr(num2str(A));
B=[6;5;1;9];          
BB=num2cell(B); 
M=containers.Map(AA,BB); 

the scale of the example is small but the real problem is huge.

i want to find the corresponding values of some point in A at the same time with less time.

请先登录，再进行评论。