Indicator matrix generation from survey questions.

indicator matrix, multiple correspondence analysis, crosstabulation analysis, categorical analysis.

Description

An indicator matrix (G), a binary coding matrix of the factors called dummy variables. The number of rows are the total sample items and the columns are the total categories of the variables. The elements in G are 1's if the item corresponding to the category of the variable or 0's if not. The indicator matrix is an alternative format to input data in a Multiple Correspondence Analysis from survey questions. One can get the Burt matrix (B) simply by B = G'G.

Syntax: function x=indmatgen(lcv,table)
     
Input:
lcv: maximum number of levels on each catagorical variable
table: table of data
             
Output:
- Indicator matrix

• MATLAB release: MATLAB 7 (R14)

[Jos]

You can use real input variables into your function, as in function x = indmatgen(lcv,table)? Also use the error function, instead of disp + return. Finally, pre-allocate your variables, and return b as an output directly, instead of copying it into x first.

[Antonio Trujillo-Ortiz]

Dear Jos. Thanks for your valuable comments for improve this m-file script. They were taken into account.

[Jos]

Again, learn how to use the function ERROR.
Secondly, avoid growing variables inside a loop. Try to pre-allocate X

Finally, this one-liner does the same
X = full(sparse(repmat(1:size(table,1),numel(lcv),1).' , bsxfun(@plus,table,[0 cumsum(lcv(1:end-1))]) , 1))

but this might be indeed to cryptic, so split it up into sub-units. Also add error checks, e.g. using for instance any(bsxfun(@gt,table,lcv))

Also take a look into SUB2IND.

In short, there is still room for improvement.