How do I read data after a specific string?
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Jason Jeong
am 24 Apr. 2017
Kommentiert: dpb
am 24 Apr. 2017
I have three sets of data: raw, average, and median. They are all in different .txt files and have 1024 data points with its x, y, z, etc.
Now I'm trying to get the data into the workspace so I can run some analysis on it but I don't know how to make a code work for the three different sets. They all start with machine and measurement specifications like date, voltage, scaling, etc. for 30-60 lines and then the data starts after three *.
Example median data_date_time
Comments and machine specifications:
... (for 30-60 lines)
Data: x, y, z, etc.
***
-8.710498,-0.039902,0.021362,-0.028009,-0.006365
-8.689081,-0.022736,0.006943,-0.027939,-0.006338
-8.667665,-0.014191,0.031357,-0.027870,-0.006311
-8.646248,-0.018768,0.033569,-0.027800,-0.006283
-8.624832,-0.029907,0.025787,-0.027731,-0.006256
-8.603415,-0.037689,0.003281,-0.027661,-0.006228
-8.581999,-0.048065,-0.009613,-0.027591,-0.006200
... (for 1024 points).
I've read some comparable questions in the forums and tried to format the answers to my problem but I've had no luck. What I do understand is that I have to read the file from the beginning, skip all 30-60 lines before *s and read the data after but I don't know how.
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Stephen23
am 24 Apr. 2017
Bearbeitet: Stephen23
am 24 Apr. 2017
opt = {'Delimiter',','};
fmt = repmat('%f',1,5);
C = {};
fid = fopen('test.txt','rt');
while ~feof(fid)
str = fgetl(fid);
if strncmp('***',str,3)
C{end+1} = textscan(fid,fmt,opt{:});
end
end
fclose(fid);
Your data is in C.
5 Kommentare
dpb
am 24 Apr. 2017
"I'm pretty sure I need the cell arrays (I need the first two columns to plot the data)."
Well, that's not a reason on its own for needing a cell array. The reason you might use a cell array is if there were multiple sets in a single file and you need to do something with more than one of these at a time but keeping them separate.
If they are in different files, there's really no reason to encapsulate the array into a cell other than that's what textscan does automgically; as I show, you may as well just cast to a simpler 2D array then and save the grief of the additional dereferencing later.
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dpb
am 24 Apr. 2017
Bearbeitet: dpb
am 24 Apr. 2017
If you don't know the number of header lines or they're variable as I gather they are, two choices:
- The easy route...see if importdata will "just work" and find the data you're looking for automagically doing the job for you for free, or
- Scan the file line-by-line until you find the magic string, then read the rest. This isn't as hard as it sounds...
fid=fopen('yourfile','r'); % open the file; be sure to add the error-checking code
l=fgetl(fid); % read first record
while ~strcmp(l,'***') % loop until find the magic record
l=fgetl(fid);
end
data=cell2mat(textscan(fid,'','collectoutput',1)); % read, convert cell to double array
fid=fclose(fid); % done with file, go on...
Now do whatever you need with the array.
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