Importing only specific entries from a text file to matlab

Question

Krish 2013-3-21

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Hello,

   I am trying to import a text file, but do not need all the information, just only specifics (after the : operator). Here is a sample version of the text file

Select type (A or B or C): C Enter the number of days: 30 Select test type (Reg or Mod): Reg Enter the number of TC's used: 1

The data is a mix of alphanumeric and numeric. So I need something that handle both. Any help will be appreciated. Thanks

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Answer 1

Cedric 2013-3-21

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编辑：Cedric 2013-3-21

在 MATLAB Online 中打开

Regular expressions are probably your best option. Look at the following:

 >> s = 'Select type (A or B or C): C Enter the number of days: 30 Select test type (Reg or Mod): Reg Enter the number of TC''s used: 1' ;
 >> results = regexp(s, '(?<=:\s+)\S+', 'match')
 results = 
    'C'    '30'    'Reg'    '1'

The second argument in the call to REGEXP is the pattern. Let me know if you need help to understand it.

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Cedric 2013-3-22

编辑：Cedric 2013-3-22

在 MATLAB Online 中打开

Krish,

 >> C = {'one', 'two', 'three', '1','2','3'}
 >> C(1)
 ans = 
    'one'
 >> class(ans)
 ans =
    cell

Here you can see that the class/type of C(1) is cell and not char. Cells are containers; to access their content, you need {} indexing:

 >> C{1}
 ans =
     one
 >> class(ans)
 ans =
     char

So C(1) gives cell #1 and C{1} gives the content of cell #1. As mentioned above, C is a 1D cell array with 6 cells. Each cell content is a string. So you are in a situation where you will just access the content of cells whose content has to be used as strings, and you will access + convert to a numeric type the content of cells whose content has to be treated as numbers.

 >> C{2}
 ans =
     two
 >> class(ans)
 ans =
     char

here you have directly a string (type=char), there is no need to convert to char.

 >> C{6}
 ans =
     3
 >> class(ans)
 ans =
     char

Now here you have a string as well, that you want to convert to a numeric type, e.g. double..

 >> str2num(C{6})
 ans =
     3
 >> class(ans)
 ans =
     double

or ..

 >> str2double(C{6})
 ans =
     3

Now you can still use () on C to extract one cell as seen above, or blocks of cells, e.g.

 >> C(4:6)
 ans = 
    '1'    '2'    '3'
 >> class(ans)
 ans =
     cell

here, we indexed the block 4:6 of the cell array C. This is a cell array as well. Now some functions are able to read the content of cells when you provide them with cell arrays instead of simply the type/class that they are meant to operate on. Typically, STR2DOUBLE can take a cell array of strings, and convert it to an array of double:

 >> str2double(C(4:6))
 ans =
     1     2     3
 >> class(ans)
 ans =
     double

Hope it helps!

Krish 2013-3-22

Got it. Sure make a difference when you have someone to take the time to explain. Its hard to figure something this simple when you have to read it from a text by yourself.

Again thanks a lot for your time and effort.

Cedric 2013-3-22

You're welcome!

Indexing is not the simplest thing to understand by ourselves actually, this is why I gave a little more explanations than usual. Paradoxically, understanding how to solve nice enough differential equations with MATLAB is simpler than understanding basic data structure and indexing.

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