Program Flow
This section describes in detail the different steps in PROC COMPUTAB
execution.
Step 1: Define Report Organization and Set Up the COMPUTAB Data Table
Before the COMPUTAB procedure reads in data or executes
programming statements, the columns list from the COLUMNS
statements and the rows list from the ROWS statements are
used to set up a matrix of all columns and rows in the report.
This matrix is called the COMPUTAB data table (CDT).
When you define columns and rows of the CDT, the COMPUTAB procedure
also sets up corresponding variables in working storage called
the program data vector (PDV) for programming statements. Data values reside in
the CDT but are copied into the program data vector as they
are needed for calculations.
Step 2: Select Input Data with Input Block Programming Statements
The input block copies input observations into rows or columns of the
CDT. By default, observations go to columns;
if the data set is not transposed (NOTRANS option),
observations go to rows of the report table.
The input block consists of all executable statements before any
ROWxxxxx: or COLxxxxx: statement label.
Use programming statements to perform calculations
and select a given observation to be added into the report.
Input Block
The input block is executed once for each observation in the
input data set. If there is no input data set, the input block is not
executed. The program logic of the input block is as follows:
- Determine which variables, row or column, are selector variables
and which are data variables. Selector variables determine which
rows or columns receive values at the end of the block. Data
variables contain the values that the selected rows or columns receive.
By default, column variables are selector
variables and row variables are data variables. If the input data
set is not transposed (NOTRANS option), the roles are reversed.
- Initialize nonretained program variables (including selector variables)
to 0 (or missing if the INITMISS option
is specified). Selector variables are temporarily associated with
a numeric data item supplied by the procedure. Using these variables
to control row and column selection does not affect any other data values.
- Transfer data from an observation in the data set to data
variables in the PDV.
- Execute the programming statements in the input block using values from the PDV and
storing results in the PDV.
- Transfer data values from the PDV into the appropriate columns of the
CDT. If a selector variable for a row or column has a
nonmissing, nonzero value, multiply each PDV value for variables used
in the report
by the selector variable and add the results to the selected row
or column of the CDT.
Step 3: Calculate Final Values Using Column Blocks and Row Blocks
Column Blocks
A column block is executed once for each row of the CDT.
The program logic of a column block is as follows:
- Indicate the current row by setting the corresponding row
variable in the PDV to 1 and the other row variables
to missing. Assign the current row number to the special variable _ROW_.
- Move values from the current row of the CDT to the
respective column variables in the PDV.
- Execute programming statements in the column block using the
column values in the PDV. Here, new columns can be
calculated and old ones adjusted.
- Move the values back from the PDV to the current row of the CDT.
Row Blocks
A row block is executed once for each column of the CDT.
The program logic of a row block is as follows:
- Indicate the current column by setting the corresponding
column variable in the PDV to 1 and the other column
variables to missing. Assign the current column number to
the special variable _COL_.
- Move values from the current column of the CDT to the
respective row variables in the PDV.
- Execute programming statements in the row block using the row
values in the PDV. Here new rows can be calculated
and old ones adjusted.
- Move the values back from the PDV to the current
column of the CDT.
See "Controlling Execution within Row and Column Blocks"
later in this chapter for details.
Any number of column blocks and row blocks can be used.
Each may include any number of programming statements.
The values of row variables and column variables are determined by the
order in which different row-block and column-block programming statements
are processed. These values can be modified throughout the COMPUTAB
procedure, and final values are printed in the report.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
