The concept of a LEAD function infers the ability to look ahead to a subsequent observation in a data set. This functionality can be obtained by using the SET statement's POINT= variable option.

By assigning an observation number to the numeric variable specified with the option, and then using the option in a second SET statement, a subsequent observation can be accessed (read into the program data vector, or PDV) in addition to the current observation.

Because a variable name can exist only once in the PDV, the second SET statement would ordinarily result in the value of the variables from the first SET statement being overwritten. To avoid this behavior, the KEEP= and RENAME= data set options should be used with the second SET statement to read in only the pertinent variables and to give them a new name.

When the POINT= option is used with a SET statement, and that specific SET statement is the only statement that reads an observation from a data set, then a STOP statement is required. The STOP statement lets the SAS^® program know when to terminate the DATA step. In this sample, the initial SET statement (without the POINT= option) reads every observation sequentially. As such, SAS will terminate the DATA step when all the observations have been read via that SET statement.

See also SAS Note 24666, "Creating the equivalent of the LEAD function by comparing the value of a variable to its value in the next observation."

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These sample files and code examples are provided by SAS Institute Inc. "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Recipients acknowledge and agree that SAS Institute shall not be liable for any damages whatsoever arising out of their use of this material. In addition, SAS Institute will provide no support for the materials contained herein.

This sample demonstrates how to read the subsequent observation in a data set in addition to the current observation during the same iteration of the DATA step. The value of a variable from the subsequent observation is subtracted from the same variable in the current observation to demonstrate this functionality. Conditional logic is included so as not to attempt to read a subsequent observation when the current observation is the last observation in the data set.

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/*Sample data set*/
data one;
  input var1 $ var2;
datalines;
A 10
B 22
C 5
D 41
E 33
;
run;

data two;
/*Add the END= option to facilitate checking for last observation.*/
  set one end=finished;
/*Look ahead only if not on last observation.*/
  if not finished then do;
/*Define or calculate the observation number to be read. In this example,*/
/*simply add one to the _N_ variable to read the very next observation.*/
  pt = _N_ + 1;
/*Be sure to keep only pertinent variables and rename them.*/
  set one (keep= var2 rename= (var2 = next_var2)) point=pt;
/*Subtract next value of var2 from current value of var2.*/
  diff = var2 - next_var2;
  end;
  else next_var2 = .;
run;

proc print; run;

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These sample files and code examples are provided by SAS Institute Inc. "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Recipients acknowledge and agree that SAS Institute shall not be liable for any damages whatsoever arising out of their use of this material. In addition, SAS Institute will provide no support for the materials contained herein.

                       next_
Obs    var1    var2     var2    diff

 1      A       10       22      -12
 2      B       22        5       17
 3      C        5       41      -36
 4      D       41       33        8
 5      E       33        .        .

The SET statement provides random access to any observation by using the POINT= option to specify a particular observation number to be read.

Type:	Sample
Topic:	SAS Reference ==> Statements ==> File-handling ==> SET ==> with POINT= SAS Reference ==> Statements ==> File-handling ==> SET SAS Reference ==> Functions ==> Special SAS Reference ==> DATA Step

Date Modified:	2020-04-20 12:14:35
Date Created:	2009-06-10 14:41:53

Operating System and Release Information

Product Family	Product	Host	SAS Release
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