Appending: Details
The APPEND Procedure
Another way to combine SAS data sets is to append one
data set to another using the APPEND procedure. Although appending
and concatenating are similar, there are some important differences
between the two methods. Whereas the DATA step creates an entirely
new data set when concatenating, PROC APPEND simply adds the observations
of one data set to the end of a “master” (or BASE) data
set. SAS does not create a new data set nor does it read the base
data set when executing the APPEND procedure.
To append SAS data sets,
you specify a BASE= data set, which is the data set to which observations
are added and then specify a DATA= data set, which is the data set
containing the observations that are added to the base data set. The
data set specified with DATA= is the only one of the two data sets
that SAS actually reads.
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Syntax, APPEND procedure:
PROC APPEND BASE=SAS-data-set
DATA=SAS-data-set;
RUN;
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For example, the following
PROC APPEND statement appends the observations in data set B to the
end of data set A:
proc append base=A
data=B;
run;Figure 13.6 How PROC APPEND Appends Data
Requirements for the APPEND Procedure
Here are the requirements for appending one data set
to another:
-
Only two data sets can be used at a time in one step.
-
The variable information in the descriptor portion of the base data set cannot change.
Note: The final data set is the
original data set with appended observations. The observations in
the BASE= data set are not read.
Example: Using the PROC APPEND Statement to Combine Data Sets
The following PROC APPEND statement appends the data
set Totals2011 to the base data set Totals2005. The two data sets
are like-structured data sets: that is, both data sets have the same
variable information.
proc append base=totals2005 data=totals2011; run;
Below is the listing
of Totals2005. The first four observations already existed in totals2005,
and the last four observations were read from totals2011 and added
to totals2005.
Figure 13.7 Example: PROC APPEND
Using the FORCE Option with Unlike-Structured Data Sets
In order to use PROC
APPEND with data sets that have unmatching variable definitions, you
can use the FORCE option in the PROC APPEND statement.
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Syntax, APPEND procedure
with the FORCE option:
PROC APPEND BASE=SAS-data-set
DATA=SAS-data-set
FORCE;
RUN;
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The FORCE option is
needed when the DATA= data set contains variables that meet any one
of the following criteria:
-
They are not in the BASE= data set.
-
They are variables of a different type (for example, character or numeric).
-
They are longer than the variables in the BASE= data set.
If the length of a variable
is longer in the DATA= data set than in the BASE= data set, SAS truncates
values from the DATA= data set to fit them into the length that is
specified in the BASE= data set.
If the type of a variable
in the DATA= data set is different from that in the BASE= data set,
SAS replaces all values for the variable in the DATA= data set with
missing values and keeps the variable type of the variable specified
in the BASE= data set.
If the BASE= data set
contains a variable that is not in the DATA= data set, the observations
are appended, but the observations from the DATA= data set have a
missing value for the variable that was not present in the DATA= data
set. If the DATA= data set contains a variable that is not in the
BASE= data set, the variable is dropped from the output.
Example: Appending with FORCE Option
proc append base=sasuser.patients
data=clinic.append force;
run; Figure 13.8 Example: PROC APPEND with FORCE Option
Last updated: January 10, 2018
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