![]() The following example iterates over a few terms in the Fibonacci sequence: The syntax in the DATA step is to specify a list of values (numeric or character) after the equal sign. SAS doesn't support that syntax directly, but there is a variant of the DO loop in which you can iterate over values in a specified list. Some languages support a "foreach loop" that iterates over objects in a collection. To prevent this behavior, use a DO loop with a WHILE clause. It is worth noting that a DO loop with an UNTIL clause always executes at least one time because the condition is evaluated at the end of the loop. SAS also supports a DO WHILE and DO UNTIL syntax that does not involve using a counter variable. Consequently, the examples have two stopping conditions: a maximum number of iterations and the WHILE or UNTIL criterion. If the condition is not satisfied when i=5 (the last value for the counter), the loop stops anyway. In these examples, the iteration stopped because the WHILE or UNTIL condition was satisfied. When i=4, the WHILE condition is not satisfied, so the loop iterates again. The following statements extend the DATA step example and iterate as long as the value of y is less than 20. The condition is checked before each iteration, which implies that you should intialize the stopping condition prior to the loop. You can use the DO statement with a WHILE clause to iterate while a condition is true. There are two ways to do this: you can use the WHILE clause to iterate as long as a certain condition holds, or you can use the UNTIL clause to iterate until a certain condition holds. On occasion, you might want to stop iterating if a certain condition occurs. Variations on the DO loop: DO WHILE and DO UNTIL As mentioned in the previous section, you can also use the BY option to increment the counter by non-unit values and by negative values. In the body of the loop, z is the sum of powers of the elements of x.ĭuring the ith iteration, the elements of x are raised to the ith power. An END statement marks the end of the loop, as shown in the following example: The basic iterative DO statement in SAS has the syntax DO value = start TO stop. Older languages, such as FORTRAN and SAS, call the iteration statement a "do loop," but it is exactly the same concept. The most well-known statement is the "for loop," which is used by C/C++, MATLAB, R, and other languages. Different languages use different keywords to define the iteration statement. Loops are fundamental to programming because they enable you to repeat a computation for various values of parameters. I'll describe looping in the SAS DATA step and compare it with looping in the SAS/IML language. Today is the first anniversary of this blog, which is named The DO Loop, so it seems appropriate to blog about DO loops in SAS. ![]() Whether you need to iterate over parameters in an algorithm or indices in an array, a loop is often one of the first programming constructs that a beginning programmer learns. We learned about three different ways to iterate or loop over a vector in reverse direction.Looping is essential to statistical programming. We iterated over all elements of a vector in reverse direction. reverse iterators, for_each() and Lambda function Iterate over a vector in backward direction using ![]() Inside the lambda function we can perform any operation like printing the elements or any other operation. If we pass the reverse iterators returned by rbegin() and rend() to for_each(), then it will iterate over the elements of vector in reverse direction and apply a lambda function on each item of the vector.
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