Statistical Data Management in MATLAB

In the Apr-08-2007 posting, Getting Data Into MATLAB Using textread, basic use of the textread function was explained, and I alluded to code which I used to load the variables names. The name-handling code was not included in that post, and reader Andy asked about it. The code in question appears below, and an explanation follows (apologies for the Web formatting).


% Specify filename
InFilename = 'C:\Data\LA47INTIME.tab';

% Import data from disk
A = textread(InFilename,'','headerlines',1, ...
'delimiter','\t','emptyvalue',NaN,'whitespace','.');

% Establish number of observations ('n') and variables ('m')
[n m] = size(A);

% Note: Load the headers separately because some software
% writes out stupid periods for missing values!!!

% Import headers from disk
FileID = fopen(InFilename); % Open data file
VarLabel = textscan(FileID,'%s',m); % Read column labels
VarLabel = VarLabel{1}; % Extract cell array
fclose(FileID); % Close data file

% Assign variable names
for i = 1:m % Loop over all variables
% Shave off leading and trailing double-quotes
VarLabel{i} = VarLabel{i}(2:end-1);

% Assign index to variable name
eval([VarLabel{i} ' = ' int2str(i) ';']);
end


After the user specifies the data file to be loaded, data is stored in array 'A', whose size is stored in 'n' and 'm'.

Next, the file is re-opened to read in the variable names. Variable names are stored two ways: the actual text names are stored in a cell array, 'VarLabel', and 1 new MATLAB variable is created as an index for each column.

To illustrate, consider a file containing 4 columns of data, "Name", "Sex", "Age" and "Height". The variable 'VarLabel' would contain those 4 names as entries. Assuming that one stores lists of columns as vectors of column indices, then labeling is easy: VarLabel(3) is "Age". This is especially useful when generating series of graphs which need appropriate labels.

Also, four new variables will be created, which index the array 'A'. They are 'Name' (which has a value of 1), 'Sex' (value: 2), 'Age' (3) and 'Height' (4). They make indexing into the main data array easy. The column of ages is: A(:,Age)

I had begun bundling this code as a function, but could not figure out how to assign the variable indices outside of the scope of the function. It is a short piece of code, and readers will likely want to customize some details, anyway. Hopefully, you find this helpful.