MATLAB: Searching for group of letters in a structure or character string

matsharkstringsstructureswireshark

Hi all,

I am working with a structure that contains various pieces of mixed data and having trouble sifting through it to find necessary pieces of info. For example, Structure(1).field contains eth:ip:udp:dns and Structure(169).field contains eth:ip:tcp.

I would like to efficiently find, for example, all elements that contain tcp.

If anyone could help out I would really appreciate it.

Thanks, Adam

Best Answer

Suppose your structure is:

S(1).field = 'eth:ip:udp:dns';
S(2).field = 'eth:ip:tcp';
S(3).field = 'eth:ip';
idx = ~cellfun('isempty',strfind({S.field},'tcp'));
S(idx)

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This could help.

MATLAB: MATLAB Execution Time Increasing despite preallocation

Here is the issue:

The string (an char array in MATLAB) packdata was being resized and reallocated over and over again. That's what was slowing down this code. I did the following steps:

1. I eliminated the redundant variable packdata and now only use eth.pack.

2. I preallocated eth.pack and a couple "helper variables" of known lengths by running blanks ONCE for each before the loop ever starts

    eth.pack = blanks(604);
    thisline = blanks(47);
    smline = blanks(32);

(Note: 604 is the maximum possible size of packdata based on headers + MODBUS protocol)

3. Then I created a pointer variable to point to the location of the last char written to packdata.

    pptr = 1;
    ...
    dataline = int16(str2double(MBLine(1:4)));
    thisline = MBLine(7:53); %Always 47 characters
    smline = [thisline(~isspace(thisline)),blanks(32-sum(~isspace(thisline)))]; %Always 32 Characters
    eth.pack(pptr:pptr+31) = smline;
    pptr = pptr + 32;

The above was inside the 'if packline > 3' block in place of the 'packdata =' statement, then at the end of the 'if stoppack' block was the reset statement:

    pptr = 1; %Reset Pointer

FYI, not surprisingly this brought out other flaws in my code which I've mostly fixed but still need to finish. Not a big issue now as this loop executes lightning fast with these changes. Thanks to Philip and dpb for helping point me in the right direction.

I kept thinking my huge table, MBTable was the issue... but it had nothing to do with it.

Best Answer

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