This is the code used: DATA drugs; Input Patient_ID Drug_ID Drug :$20; Datalines; 9900001 1 vinorelbine 9900001 2 carboplatin 9900001 2 paclitaxel 9900003 1 fluorouracil 9900005 1 5-FU 9900005 1 leucovorin 9900005 2 fluorouracil 9900005 3 fluorouracil 9900005 3 leucovorin 9900008 1 fluorouracil 9900008 2 fluorouracil 9900008 2 leucovorin 9900008 3 fluorouracil 9900008 3 irinotecan 9900008 3 leucovorin ; RUN; Data Drug_combo (DROP=drug); DO until (last.drug_ID); SET drugs; BY Patient_ID Drug_ID; LENGTH drug_combo $200; drug_combo= catx('', drug_combo, drug); end; RUN; My log: 1 OPTIONS NONOTES NOSTIMER NOSOURCE NOSYNTAXCHECK; 68 69 DATA drugs; 70 Input Patient_ID Drug_ID Drug :$20; 71 72 Datalines; NOTE: SAS went to a new line when INPUT statement reached past the end of a line. NOTE: The data set WORK.DRUGS has 14 observations and 3 variables. NOTE: DATA statement used (Total process time): real time 0.00 seconds user cpu time 0.00 seconds system cpu time 0.00 seconds memory 669.78k OS Memory 23976.00k Timestamp 10/25/2022 10:23:33 PM Step Count 24 Switch Count 2 Page Faults 0 Page Reclaims 167 Page Swaps 0 Voluntary Context Switches 13 Involuntary Context Switches 0 Block Input Operations 0 Block Output Operations 264 89 ; 90 91 RUN; 92 93 Data Drug_combo (DROP=drug); 94 DO until (last.drug_ID); 95 SET drugs; 96 BY Patient_ID Drug_ID; 97 LENGTH drug_combo $200; 98 drug_combo= catx('', drug_combo, drug); 99 end; 100 RUN; NOTE: There were 14 observations read from the data set WORK.DRUGS. NOTE: The data set WORK.DRUG_COMBO has 9 observations and 3 variables. NOTE: DATA statement used (Total process time): real time 0.00 seconds user cpu time 0.01 seconds system cpu time 0.00 seconds memory 1070.75k OS Memory 24236.00k Timestamp 10/25/2022 10:23:33 PM Step Count 25 Switch Count 2 Page Faults 0 Page Reclaims 210 Page Swaps 0 Voluntary Context Switches 13 Involuntary Context Switches 0 Block Input Operations 0 Block Output Operations 264 101 102 103 104 105 106 OPTIONS NONOTES NOSTIMER NOSOURCE NOSYNTAXCHECK; 116 My output: Obs Patient_ID Drug_ID Drug 1 9900008 3 c 2 9900008 2 c 3 9900008 2 n 4 9900008 1 c 5 9900008 3 n 6 9900008 3 n 7 9900005 3 c 8 9900005 2 c 9 9900005 1 9 10 9900005 3 n 11 9900003 1 c 12 9900001 2 l 13 9900001 1 n 14 9900001 2 i
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