MATLAB Central Newsreader - read

read

nachiketha Kukkady — Mon, 17 Aug 2009 01:48:01 -0400

Hi....
I've a matlab file which contains few numbers(float) in about 75 lines...
how do i read a individual line so that i can later process with these obtained numbers from some particular lines...
i did try with fgetl but that gives only the first line.. or maybe i couldn't use it properly....
could somebody help me with this??
Thank you in advance....

Re: read

dpb — Mon, 17 Aug 2009 01:58:13 -0400

nachiketha Kukkady wrote:
> Hi.... I've a matlab file which contains few numbers(float) in about
> 75 lines... how do i read a individual line so that i can later
> process with these obtained numbers from some particular lines... i
> did try with fgetl but that gives only the first line.. or maybe i
> couldn't use it properly.... could somebody help me with this?? Thank
> you in advance....

Typically fgetl() is used in a loop.

Alternatively, w/ ML it may be simpler and just as quick to read the
whole array and then discard the portion you don't want.

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Re: read

Skeptic — Mon, 17 Aug 2009 02:03:39 -0400

On Aug 16, 9:48 pm, "nachiketha Kukkady" <nachike...@in.com> wrote:
> Hi....
> I've a matlab file which contains few numbers(float) in about 75 lines...
> how do i read a individual line so that i can later process with these obtained numbers from some particular lines...
> i did try with fgetl but that gives only the first line.. or maybe i couldn't use it properly....
> could somebody help me with this??
> Thank you in advance....

-------------------------------------------------------------------------
Yeah, that's probably it (you didn't use it properly) - keep trying
(or else show us your data file and your code). You can also try
other things like fread(), fscanf(), or similar functions.

Re: read

nachiketha Kukkady — Mon, 17 Aug 2009 02:17:04 -0400

dpb <none@non.net> wrote in message <h6adn3$mg7$1@news.eternal-september.org>...
> nachiketha Kukkady wrote:
> > Hi.... I've a matlab file which contains few numbers(float) in about
> > 75 lines... how do i read a individual line so that i can later
> > process with these obtained numbers from some particular lines... i
> > did try with fgetl but that gives only the first line.. or maybe i
> > couldn't use it properly.... could somebody help me with this?? Thank
> > you in advance....
>
> Typically fgetl() is used in a loop.
>
> Alternatively, w/ ML it may be simpler and just as quick to read the
> whole array and then discard the portion you don't want.
>
> --

Thank you for that reply....
Yeah i've already the whole page or file containing those numbers....
my file is something like this.....
259.975 262.41
269.273 338.54
276.828 369.921
287.87 404.79
306.466 435.59
330.874 461.161
364.581 480.338.............
i will be needing line 2, line 5 and so on for further calculations....
As i said i've read the file using fread command.... but i don't know how exactly to remove the lines which i don't need.....
thank you....

Re: read

arun — Mon, 17 Aug 2009 02:33:25 -0400

On Aug 17, 4:17 am, "nachiketha Kukkady" <nachike...@in.com> wrote:
> dpb <n...@non.net> wrote in message <h6adn3$mg...@news.eternal-september.org>...
> > nachiketha Kukkady wrote:
> > > Hi.... I've a matlab file which contains few numbers(float) in about
> > > 75 lines... how do i read a individual line so that i can later
> > > process with these obtained numbers from some particular lines... i
> > > did try with fgetl but that gives only the first line.. or maybe i
> > > couldn't use it properly.... could somebody help me with this?? Thank
> > > you in advance....
>
> > Typically fgetl() is used in a loop.
>
> > Alternatively, w/ ML it may be simpler and just as quick to read the
> > whole array and then discard the portion you don't want.
>
> > --
>
> Thank you for that reply....
> Yeah i've already the whole page or file containing those numbers....
> my file is something like this.....
> 259.975 262.41
> 269.273 338.54
> 276.828 369.921
> 287.87 404.79
> 306.466 435.59
> 330.874 461.161
> 364.581 480.338.............
> i will be needing line 2, line 5 and so on for further calculations....
> As i said i've read the file using fread command.... but i don't know how exactly to remove the lines which i don't need.....
> thank you....

You have the whole matrix here. you can just access the essential
entries then.

fn = <path to file>';
fid = fopen(fn, 'r');
%preallocate variable if you know the number of rows and columns
a = cell(6,2); % file contains first six lines of the sample you
posted above, with 2 columns.
i=1;
while ~feof(fid),
a(i,:) = regexp(fgetl(fid),'\s', 'split'); %check for space.
i = i + 1;
end
a= cellfun(@str2num, a, 'uni', false); % conver to double array.
fclose(fid);

best, arun.

Re: read

nachiketha Kukkady — Mon, 17 Aug 2009 03:00:19 -0400

thank you....
but this is doing the same work which is being done by fread right????
what i need is get some required lines like 20th, 34th,56th and so on and finally do some processings with it.... i don't want to use the loop here...
So what can i do now????

Re: read

arun — Mon, 17 Aug 2009 03:26:07 -0400

On Aug 17, 5:00 am, "nachiketha Kukkady" <nachike...@in.com> wrote:
> thank you....
> but this is doing the same work which is being done by fread right????
> what i need is get some required lines like 20th, 34th,56th and so on and finally do some processings with it.... i don't want to use the loop here...
> So what can i do now????

what would be the problem to do it like this from the 'a' obtained
above?
ix = [23 34 45 56]
a = a(ix,:);

file pointer does not give the line number it is in, at least as far
as I know. So, if you want to do this, you must either have full and
absolute information about the format of your file data and probably
use it to calculate the number of byes on each line and then add that
much to your file pointer using feek or have some sort of header
information for the lines you require, to identify them. its a tedious
job and probably slower if your file is too big.

best, arun.

Re: read

nachiketha Kukkady — Mon, 17 Aug 2009 03:30:18 -0400

hi...
i also found one more command called 'importdata'.... can i use this to read a particular line???

Re: read

dpb — Mon, 17 Aug 2009 13:51:47 -0400

nachiketha Kukkady wrote:
...
> what i need is get some required lines like 20th, 34th,56th and so on
> and finally do some processings with it.... i don't want to use the
> loop here...
> So what can i do now????

>> x=rand(4); % some sample data
x =
     0.9501 0.8913 0.8214 0.9218
     0.2311 0.7621 0.4447 0.7382
     0.6068 0.4565 0.6154 0.1763
     0.4860 0.0185 0.7919 0.4057
>> idx=[1,3]
idx =
      1 3
>> y = x(idx,:)
y =
     0.9501 0.8913 0.8214 0.9218
     0.6068 0.4565 0.6154 0.1763
>> notx=[2 4]
notx =
      2 4
>> x(notx,:) = []
x =
     0.9501 0.8913 0.8214 0.9218
     0.6068 0.4565 0.6154 0.1763
>>

Read up on colon operator and logical indexing...

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