reshape a char array

Question

Laura 2020-2-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/507759-reshape-a-char-array

评论： Guillaume 2020-2-26

采纳的回答： David Hill

在 MATLAB Online 中打开

Hi,

I have the following MWE and I don't understand what matlab is producing:

I start with a simple 21-length char array:

ex = 'caggtgcagctggtgcagtct'

that I would like to reshape into a 7-by-3 array. Of course, I could use a loop for this, but I thought that I could just reshape it. However, when I do

reshape(ex, [7,3])
ans =
  7×3 char array
    'cag'
    'agc'
    'gca'
    'gtg'
    'tgt'
    'ggc'
    'ctt'
   

This makes no sense to me. I was expecting

'cag'
'gtg'
'cag'
'ctg'
'gtg'
'cag'
'tct'

I also tried reshape(ex, 7,3) and reshape(ex(:), 7, 3) without any luck. What is matlab doing? TIA

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Guillaume 2020-2-26

Matlab is column major. This means that when you reshape something into something else, the something else is filled column by column, not row by row. So, indeed as David shows, to get the output you want you reshape then transpose.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

David Hill 2020-2-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/507759-reshape-a-char-array#answer_417502

在 MATLAB Online 中打开

reshape(ex,[3,7])';

First number is row and second is column. Matrix is numbered down first.

2 个评论
显示无隐藏无

Laura 2020-2-26

编辑：Laura 2020-2-26

wow, that is really counter-intuitive. I guess I am used to other programming languages (i.e. python) that do not "number down first"...

Thank you!

Guillaume 2020-2-26

You'll find a number of languages (C-based mostly) are row majors and an equivalent number are column-major (Matlab, Fortran, and other math-focused languages) while a few can't make their mind up (eg. OpenGL).

So, it's only counterintuitive if you've never been exposed to the other side.

请先登录，再进行评论。