extract first 4 letters from a string in matlab

How can 开发者_如何学CI extract the first 4 or the middle 4 or last four letters of a string example: when the string reads 01 ED 01 F9 81 C6?

A string is treated like a vector of chars. Try this:

>> string = '01 ED 01 F9 81 C6'; 
>> string(1:5), string(6:11), string(12:17)

ans =
01 ED

ans =
 01 F9

ans =
 81 C6

string in this example is a variable not a method. string(1) returns the first char in the array (or vector) called string.

If you want only the non-whitespace characters you could use the ISSPACE function to remove the whitespace and then character array indexing to access the characters:

>> s = '01 ED 01 F9 81 C6';
>> s = s(~isspace(s))

s =

01ED01F981C6

>> s(1:4)

ans =

01ED

>> s(5:8)

ans =

01F9

>> s(9:end)

ans =

81C6

You can expand this to process multiple lines of a character array using RESHAPE to transform the result of the space removal back to a 2D-array and then referencing the extra dimension:

 s = ['01 ED 01 F9 81 C6'; 'F8 CA DD 04 44 3B']

s =

01 ED 01 F9 81 C6
F8 CA DD 04 44 3B

>> s = reshape(s(~isspace(s)), size(s, 1), 12)

s =

01ED01F981C6
F8CADD04443B

>> s(:,1:4)

ans =

01ED
F8CA

>> s(:,5:8)

ans =

01F9
DD04

>> s(:,9:end)

ans =

81C6
443B

As trolle3000 and b3 mentioned, you use brackets containing indices to extract subsets of the string.

To answer the additional question of how you work on the string, I suggest that you split the string at each space, and convert from hexadecimal to decimal numbers.

s = '01 ED 01 F9 81 C6';
hex2dec(regexp(s, ' ', 'split'))

ans =   
     1
   237
     1
   249
   129
   198