Hi all, I have a dataset which includes 84 rows and 4313 columns. Starting from the 2nd row, each row represents a patient. The 1st column is for "arrayID" 2nd column is for "time" 3rd column is for "cancer" 4th column is for "patientID" Starting for the 5th columns, each column's ID is like "CTC_232B23", "RP11_181G12", "RP11_62M23"... I extract first 5 rows and 7 columns and get the data in below: arrayID time cancer patientID CTC_232B23 RP11_181G12 RP11_62M23 X1747_4224 37.633 0 30635 -0.02665 -0.02665 -0.038025 X1750_4214 89.300 0 22158 -0.02665 -0.02665 -0.038025 X1751_4208 53.333 0 31669 -0.02665 -0.02665 -0.038025 X1754_4194 39.467 0 32849 -0.02665 -0.02665 -0.038025 X1775_4497 84.900 0 33563 -0.02665 -0.02665 -0.038025 Finally I would like to build the cox model for each column (starting from the 5th column). The code would be like: mod.allison <- coxph( Surv(time, cancer) ~ CTC_232B23 , data=Rossi2) mod.allison <- coxph( Surv(time, cancer) ~ RP11_181G12 , data=Rossi2) mod.allison <- coxph( Surv(time, cancer) ~ RP11_62M23 , data=Rossi2) I have no problem getting the result. However, since there are 4309 columns (counted begining at the 5th column), I decide to make a 4309*1 matrix (called "BACs") to store the name of each column. Then run a loop like: for (i in 1:4309){ mod.allison <- coxph( Surv(time, cancer) ~ BAC[i,1], data=Rossi2) } mod.allison However, I got the error. Would you like to give me some suggestions about this? Many thanks in advance! [[alternative HTML version deleted]]