matlab reading mixed data from file - matlab

Question

I am pretty new to matlab. I've been reading the documentation but can figure it out why matlab does not correctly read the string from file. What I am trying to do is to read a mixed data type from file. Some sample data is:
t a e incl lasc aper meanan truean rupnode rdnnode name
0.000000 1.2712052487 0.8899021688 22.2458 265.2511471042 322.1539251184 -13.6281352271 -130.986 0.155342 0.889756 phaet_000018
0.000000 1.2712052478 0.8899021575 22.2458 265.2511428392 322.1539270642 -13.6281369694 -130.986 0.155342 0.889756 phaet_000044
0.000000 1.2712052496 0.8899021868 22.2458 265.2511587897 322.1539149438 -13.6281365049 -130.986 0.155342 0.889755 phaet_000006
The first line is header. So here is what I've done so far:
fid = fopen('data.dat');
header = fgetl(fid); # I read the header
Now I read the data:
data = fscanf(fid,'%f %f %f %f %f %f %f %f %f %f %s',[11 inf]);
data1 = data';
fclose(fid);
I can now access the first element as:
data1(1,1)
However, when I do:
data(1,11)
instead of phaet_000018 I am getting a number (112). Any idea what I am doing wrong?

Answer 1

There are a few issues with your code.
First, your sizeA input to fscanf is backwards. sizeA with a vector input is defined as:
Read at most m*n numeric values or character fields. n can be Inf, but m cannot. The output, A, is m-by-n, filled in column order.
So you've asked fscanf to give you 11 rows and whatever number of columns. You can't have an Inf row specification so you'll want to remove the third input entirely and reshape your data afterwards.
For example:
fid = fopen('data.dat');
header = fgetl(fid);
data = fscanf(fid,'%f %f %f %f %f %f %f %f %f %f %s');
fclose(fid);
% We just happen to know this explicitly, not knowledge to generally assume
ncols = 22;
% Reshape and transpose
data = reshape(data, ncols, []).';
Gives us a 3 x 22 data array, which is kinda sorta what we want.
So where are the extra columns coming from? For %s fields, fscanf reads the string until it encounters whitespace. Because the output of fscanf is a numeric array it must convert this string into a numeric value, so it converts each character to its numeric equivalent (double(letter)) and outputs that into the matrix.
Using our above data matrix as an example, we have:
>> char(data(1, 11:end))
ans =
phaet_000018
With this in mind, your initial code only happens to work because all of your strings are the same length. If we change the length of one or more of the strings, this data import will fail:
Error using reshape
Product of known dimensions, 22, not divisible into total number of elements, 65.
Error in testcode (line 11)
data = reshape(data, ncols, []).';
So what can we do instead? If you need this string from your data I would recommend trying textscan:
fid = fopen('data.dat');
header = fgetl(fid);
data = textscan(fid, '%f %f %f %f %f %f %f %f %f %f %s');
fclose(fid);
This will read your data into a 1x11 cell array, where each column corresponds to a column in your data:
>> data{1} % t
ans =
0
0
0
To collect your numeric data you can iterate through the cell array, or you can use the 'CollectOutput' flag in textscan:
fid = fopen('data.dat');
header = fgetl(fid);
data = textscan(fid, '%f %f %f %f %f %f %f %f %f %f %s', 'CollectOutput', true);
fclose(fid);
Which will output a 1x2 cell array, where data{1} is your numeric array and data{2} is a cell array containing your strings:
>> data{1} % Numeric data
ans =
0 1.2712 0.8899 22.2458 265.2511 322.1539 -13.6281 -130.9860 0.1553 0.8898
0 1.2712 0.8899 22.2458 265.2511 322.1539 -13.6281 -130.9860 0.1553 0.8898
0 1.2712 0.8899 22.2458 265.2512 322.1539 -13.6281 -130.9860 0.1553 0.8898
>> data{2} % Strings
ans =
3×1 cell array
'phaet_000018'
'phaet_000044'
'phaet_000006'