vlt.stats.lm_category

  LM_CATEGORY - calculate a linear model for a variable measured in different fixed categories

  LM = LM_CATEGORY(TBL, CATEGORIES_NAME, Y_NAME, Y_OP, REFERENCE_CATEGORY, [RANKORDER])

  Create a linear model of the property Y_NAME that occurs in a column in 
  the table TBL. The model fits Y as a function of the categories listed in
  the TBL column CATEGORIES_NAME, using REFERENCE_CATEOGORY as a reference.
  The raw values in the table are processed through Y_OP, which evaluates a 
  column of Y elements.
  If RANKORDER is provided and is 1, then the ranks (sort order) values of
  Y are used instead of the raw values.


  Example:
   load carsmall
   tbl = table(Model_Year,MPG);
   Y_op = 'Y'; % just use Y
   % compute standard linear model
   lm = vlt.stats.lm_category(tbl,'Model_Year','MPG',Y_op,'70',0)
   % compute non-parametric linear model
   lm_ = vlt.stats.lm_category(tbl,'Model_Year','MPG',Y_op,'70',1)