How does one create an array of strings in a loop? In a better way.

Question

Samyukta Ramnath 2013-6-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/78372-how-does-one-create-an-array-of-strings-in-a-loop-in-a-better-way

评论： Cedric 2013-10-19

So I have an array of characters, separated by whitespaces, and obviously matlab recognizes whitespaces as a character too. I wanted to separate the words into strings and put them into one array so that calling a certain index would refer to the entire word. This was my code to do so.

if true
  % code
end
File1 = fopen('History2.txt');
words = fscanf(File1 , '%c');
num_words = 1;
i = 1;
new_words = char(100,1);
while(1)
      if words(i) ==' '
          num_words = num_words+1;
      else
          new_words(num_words, i) = words(i);
      end
      if words(i+1)=='9'
          num_words = num_words - 2;
          break;
      end
      i=i+1;
  end  
  if true
    % code
  end

Now, this does the job as in I can refer to the word by saying new_words(1, :). But, the way it displays is it as such :

OUTPUT: Hello, history tells us that history ... ... and so on. Moreover, when I want to compare two of the strings, using strfind like this:

if ~(isempty (strfind ( new_words(2,:) , new_words(6,:) ) ) )
  disp('yoyo');
else
  disp('nono');
end

It always displays 'nono'. What is a better way to accomplish this task so that I can perform the comparison between the strings to find the unique words in the paragraph?

Maybe using cell arrays? But how would I do that, given the words?

I even tried using strsplit, but this wouldn't work on the array words.

9 个评论
显示 7更早的评论隐藏 7更早的评论

Marc 2013-10-19

在 MATLAB Online 中打开

Cedric

If you type edit strsplit in 2013a/b check line 80 and 83. It looks like this:

if ~isString(str)
    error(message('MATLAB:strsplit:InvalidStringType'));
end
if isString(aDelim)
    aDelim = {aDelim};
elseif ~isCellString(aDelim)
    error(message('MATLAB:strsplit:InvalidDelimiterType'));
end

This is straight from the Matlab toolbox... (Matlab/toolbox/Matlab/strfun) So I am not sure what you are talking about with respect to isString... Although I agree that if I type edit isString I get an error that it is not on any path. So, you got me why this function works. I chalk it up to Matlab Magic.

Line 119 and 120 calls regexp... Not sure why you think that strsplit would be faster since it calls regexp... This line was also how I fell into the regexp route.

% Split.
[c, matches] = regexp(str, aDelim, 'split', 'match');

Cedric 2013-10-19

编辑：Cedric 2013-10-19

在 MATLAB Online 中打开

Ah! My mistake, 2013a/b have STRSPLIT but not the 2012b on my laptop. Yet, ISTRING doesn't seem to be a built-in. Isn't it an internal function in STRSPLIT? I can't check now but I could check on Monday.

STRFUN is not a regular\base MALTAB toolbox (available separately here).

Your last point about STRSPLIT calling REGEXP is why I wrote "good implementation" in my previous comment. Well, "good" is a question of point of view, but what I had in mind was that an easy implementation is to write STRSPLIT as a wrapper for REGEXP (which is what you discovered), and that a "good" implementation would be more specific and efficient. I mentioned the difference in efficiency between STRREP and REGEXPREP to illustrate this point: an easy implementation of STRREP would be a wrapper for REGEXPREP, but the MATLAB implementation of STRREP if more specific and efficient:

 >> testStr = repmat('AB ', 1, 1e5) ;
 >> tic ;  strrep(testStr, 'A', 'CC') ;  toc
 Elapsed time is 0.002794 seconds.
 >> tic ;  regexprep(testStr, 'A', 'CC') ;  toc
 Elapsed time is 4.176688 seconds.