MATLAB: How to import a particular text file and plot.

Question

Here is the data that I wish to import:

Scan(+/- seconds),Sensor1Value,Sensor2Value,Sensor3Value,Sensor4Value

-1, 2, 8, 3, 4

'#' Comment Here

9, 0, 5, 6, 7

————————————-

If I want to plot this kind of data,

fid = fopen(file.txt');

% read column headers

header = textscan(fid, '%s', 5, 'delimiter', ',', … 'commentStyle', '#');

% read numeric data

data = textscan(fid, '%f %f %f %f %f', 'delimiter', ',', … 'commentStyle', '#');

fclose(fid);

————

My question is, when I type in header{1} I get all five columns. Shouldn't it be the case that if I type in header{1}, header{2}, header{3},…,header{5} I should get: Scan, Sensor1Value, Sensor2Value,…,Sensor4Value respectively?

Answer 1

By specifying a format string of '%s', you effectively asked textscan for a single output. But then you asked to read a string 5 times. Consequently output is a single cell which contains five things. Those five things are themselves cells, which contain the strings you want. (Confused?)

So to get the third header, do

header{1}{3}

Or, you could do

textscan(fid, '%s%s%s%s%s', 1, ...

In which case you will get back 5 cells. But then each of them contains a single cell (which contains a string)!

Unfortunately this is just the way textscan works. It makes sense for reading whole columns of data, but not so much for a header line.

You can always do what you were doing and add

header = header{1}

Or do it the other way I showed above and add

header = [header{:}]

Either way, then, header will be a 5-element cell array of the strings.

EDIT, attempting to clarify: textscan returns an n-element cell array, where n is the number of format specifiers in the format string. Each cell will contain the contents that were read from the file. If the contents were numeric, you'll just get a numeric array. But if they were strings, you'll get a cell array of strings. That's why you're ending up with cell arrays containing cell arrays.