 Usage:  nar = haznar(data)  
 
 Input:

  data                   n x (p+4) matrix, 
                         column 1: the sorted observed survival time t, 
                         column 2: the cosorted censoring indicator delta, 
                         column 3: labels l, 
                         column 4: number of ties at time t[i], cosorted, 
                         columns 5 to p+4: the cosorted covariate matrix z. 
                         
 Output:

  nar                    n x 1 vector, the ith entry is the size of the 
                         risk set at time t_i. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
