Arrays, transposing data with

There are two tools commonly used for performing data transpositions in SAS PROC TRANSPOSE, and a DATA step with ARRAY statements. PROC TRANSPOSE is a powerful tool that flips a data set with just a few lines of SAS code. On the other hand, DATA steps that employ arrays for data transposition are more flexible, in that they allow for more precise control of the transposition process. We will now examine PROC... 

There may be times when a DATA step with arrays is a better means to transpose data. This is true when the data to be transposed have more than one record per BY group variable or when there is a need to have the resulting data set include data that are not in the source data set. In clinical trials missing data is a very common issue. Let s look at a derivation of the previous systolic blood pressure transposition problem where visit 2 is always missing. 

In an Excel spreadsheet, the [TRANSPOSE function can be applied to an array of data. For this, we need to become familiar with the two most important rules to perform matrix operations in Excel ... 

Notice the missing column for visit 2. This is exactly what you would expect PROC TRANSPOSE to give you. PROC TRANSPOSE transposed the data that were present and could not be expected to know about visits that are not represented in the data. However, often in clinical trials reporting you want to report on all visits, treatments, or other expected parameters whether they are represented in the actual data or not. In this case, a DATA step with arrays is a better choice to transform the data. Here is an example of the previous transposition that includes all visits 1-5, regardless of which visits are included in the underlying data. 

PROC TRANSPOSE is an efficient way to transpose a SAS data set when the transposition process is simple. However, if the transposition process is more complicated, and involves transforming to a data set where all possible columns must be represented or where there are multiple records per BY group, then a DATA step with arrays is probably a better choice. 

A fourth matrix operation, TRANSPOSE, is performed as part of the Edit => Paste Special operation. 2 Matrix inversion and matrix multiplication work only on data arrays, i.e., rectangular blocks of cells, but not on single cells. To enter these instructions, enter the array with CRTL + SHIFT + ENTER (on the Macintosh COMMAND + RETURN). 

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