08-29-2017 10:26 AM
Hi I am studying for the Base Certification Exam and I have a quetion over Assignment Statement, Sum Statement, Sum Function, and missing values. Assignment Statements are all statements in the form of A=a+b and will always produce a missing value if a missing value is present in the data, correct? Sum statements a+b and sum functions sum(of a,b) will ignore missing values if present in the data, correct? If a statement consists of a combination of the two Avg=mean(of a,b) this is ultimately in the form of an assignment statement so the missing value would produce missing data for the remaining output - is this correct?
I appreciate any help or reference you can provide me for clarification on this material.
Thanks!
08-29-2017 10:43 AM
You were doing great until you got to the MEAN function. The MEAN function ignores missing arguments, and computes the mean of the non-missing arguments.
08-29-2017 10:43 AM
Look up each statement and review it's specific documentation.
https://support.sas.com/documentation/cdl/en/lestmtsref/69738/HTML/default/viewer.htm#titlepage.htm
08-29-2017 10:43 AM
You were doing great until you got to the MEAN function. The MEAN function ignores missing arguments, and computes the mean of the non-missing arguments.
08-29-2017 11:41 AM
Thank you!
08-29-2017 10:44 AM
You could write a simple data step and see what happens.
There is no need ot use of in sum or mean function while not using wildcards. The functions sum and mean ignore missing values.
data work.test;
input a b;
c = a + b;
d = sum(a, b);
e = mean(a, b);
f = a;
g = b;
f + g;
label
c = 'a+b'
d = 'sum(a, b)'
e = 'mean(a, b)'
f = 'f=b; f+g'
g = 'b'
;
datalines;
. 1
1 .
1 1
. .
;
run;
proc print data=work.test label;
run;
08-29-2017 11:30 AM
Hello KMJ,
You are correct. Assignment statements result in NULL if any operand is a NULL value. Sum statements and Sum functions do ignore NULL values in their final result. Regarding your last question, The functions, operands and operators on the right side of the equation drive the result. In your example, AVG is assigned the result since the MEAN function parameters that are NULL are ignored. If you tried to subtraction or add a NULL value, AVG=MEAN(of a1=a4) - null_val, then the AVG would be NULL.
This code demonstrates each of your questions:
DATA x;
*** Assignment question ***;
x=10;
y=.;
A=x+y;
PUT "=================";
PUT A= ;
*** SUM() Question ***;
d1=10;
d2=20;
d3=30;
d4=.;
D=SUM( of d1-d4);
PUT D=;
*** Combining Assignment and Function statements Question***;
E=MEAN(of d1-d4);
PUT E=;
F=MEAN(of d1-d4) - d4;
PUT F=;
PUT "=================";
RUN;
*** SUM Statement Question***;
DATA x2;
INFILE DATALINES;
LENGTH val 8;
INPUT val ;
val_sum + val; ** <- sum statement **;
DATALINES;
10
20
30
.
;
RUN;
PROC PRINT; RUN;
DATALINES;
10
20
30
.
;
RUN;
PROC PRINT; RUN;
========================LOG=====================
========================OUTPUT=====================
Obs | val | val_sum |
1 | 10 | 10 |
2 | 20 | 30 |
3 | 30 | 60 |
4 | . | 60 |
08-29-2017 11:41 AM
Thank you so much this was helpful.
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