Handout06 - Lecture 6 1 Repetitive code 2 Arrays 3 Macros 1...

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Lecture 6 1. Repetitive code 2. Arrays 3. Macros 1 Repetitive code Often we want to repeat the same operation on a list of variables: compare 15 characteristics between 3 groups. Example. A nutrition clinical study compared three Fber supplements—barley, oats, control—in a parallel-arm design. Primary outcomes were changes from baseline to study midpoint and endpoint in blood lipids, stress markers, glucose and insulin. Outcome = change from baseline for each of 7 measurements. ¢ y = change in y = Fnal value y F ° baseline value y 0 positive ¢ y means an increase, negative ¢ y means a decrease. 2
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Alphabetic List of Variables and Attributes #V a r i a b l e T y p eL e nF o r m a tI n f o r m a tL a b e l 3A g e N u m 8 A g e 9 Base_CRP Num 8 Base CRP 6 Base_Chol Num 8 Base Chol 11 Base_Gluc Num 8 Base Gluc 10 Base_HCYS Num 8 Base HCYS 7B a s e _ H D L N u m 8 B a s e H D L 8B a s e _ L D L N u m 8 B a s e L D L 5B a s e _ T G N u m 8 B a s e T G 22 Final_CRP Num 8 Final CRP 19 Final_Chol Num 8 Final Chol 24 Final_Gluc Num 8 Final Gluc 23 Final_HCYS Num 8 Final HCYS 20 Final_HDL Num 8 Final HDL 21 Final_LDL Num 8 Final LDL 18 Final_TG Num 8 Final TG 1I D N u m 8 I D ... (more) 3 A simple direct approach is to write down all the subtractions: data one; set pubh.barley; dm_chol = Mid_Chol - base_chol; dm: d for delta, m for midpoint dm_TG = Mid_TG - Base_TG; dm_HDL = Mid_HDL - Base_HDL; dm_LDL = Mid_LDL - Base_LDL; dm_CRP = Mid_CRP - Base_CRP; dm_HCYS = Mid_HCYS - Base_HCYS; dm_Ins = Mid_Ins - Base_Ins; dm_Gluc = Mid_Gluc - Base_Gluc; Another block for change from baseline to Fnal value. Use Control-H search and replace. 4
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data one; set pubh.barley; dm_chol = Mid_Chol - base_chol; dm_TG = Mid_TG - Base_TG; dm_HDL = Mid_HDL - Base_HDL; dm_LDL = Mid_LDL - Base_LDL; dm_CRP = Mid_CRP - Base_CRP; dm_HCYS = Mid_HCYS - Base_HCYS; dm_Ins = Mid_Ins - Base_Ins; dm_Gluc = Mid_Gluc - Base_Gluc; df_chol = final_Chol - base_chol; df_TG = final_TG - Base_TG; df_HDL = final_HDL - Base_HDL; df_LDL = final_LDL - Base_LDL; df_CRP = final_CRP - Base_CRP; df_HCYS = final_HCYS - Base_HCYS; df_Ins = final_Ins - Base_Ins; df_Gluc = final_Gluc - Base_Gluc; Hard to check. 5 Data step: Arrays ( LSB §3.11) An array is a vector or matrix of variables In a data step, to create a vector array: ARRAY array_name [ number of variables ] variable list ; In a data step, to create a matrix array: ARRAY array_name [ number of rows, number of columns ] list of row 1 variables, row 2 variables, etc ; Whenever you are repeating the same calculation more than twice, consider using arrays.
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Handout06 - Lecture 6 1 Repetitive code 2 Arrays 3 Macros 1...

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