Using first.variable and last.variables with accumulator variables
I am trying to understand what this program does.
data a;
set b (keep=c d);
by c;
if first.c then e=0;
e+d;
if last.c;
run;
What confuses me is the following.
1), When there is not THEN statements, what does and IF statement do?
2), When there is no value evalueated, what does an IF statement do ? (why would it not say something like if first.c =1 ?)
3), My understanding is that e is an accumulator variable starting from 0, and d is added by iteration. But for some reason e represents the total for all values of c, not d even though we are adding d.
I am thinking that the first two questions will answer my question 3, but I would really appreciate your help.
sas
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
add a comment |
I am trying to understand what this program does.
data a;
set b (keep=c d);
by c;
if first.c then e=0;
e+d;
if last.c;
run;
What confuses me is the following.
1), When there is not THEN statements, what does and IF statement do?
2), When there is no value evalueated, what does an IF statement do ? (why would it not say something like if first.c =1 ?)
3), My understanding is that e is an accumulator variable starting from 0, and d is added by iteration. But for some reason e represents the total for all values of c, not d even though we are adding d.
I am thinking that the first two questions will answer my question 3, but I would really appreciate your help.
sas
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
1
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out theif last.c;statement and changingif first.c then e=0toif first.c=1 then e=0, to see if/how they change the output. Also try addingput (c d e)(=);aftere+d;
– Quentin
Nov 14 '18 at 14:10
add a comment |
I am trying to understand what this program does.
data a;
set b (keep=c d);
by c;
if first.c then e=0;
e+d;
if last.c;
run;
What confuses me is the following.
1), When there is not THEN statements, what does and IF statement do?
2), When there is no value evalueated, what does an IF statement do ? (why would it not say something like if first.c =1 ?)
3), My understanding is that e is an accumulator variable starting from 0, and d is added by iteration. But for some reason e represents the total for all values of c, not d even though we are adding d.
I am thinking that the first two questions will answer my question 3, but I would really appreciate your help.
sas
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
I am trying to understand what this program does.
data a;
set b (keep=c d);
by c;
if first.c then e=0;
e+d;
if last.c;
run;
What confuses me is the following.
1), When there is not THEN statements, what does and IF statement do?
2), When there is no value evalueated, what does an IF statement do ? (why would it not say something like if first.c =1 ?)
3), My understanding is that e is an accumulator variable starting from 0, and d is added by iteration. But for some reason e represents the total for all values of c, not d even though we are adding d.
I am thinking that the first two questions will answer my question 3, but I would really appreciate your help.
sas
sas
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
asked Nov 13 '18 at 7:57
hyg17hyg17
1639
1639
1
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out theif last.c;statement and changingif first.c then e=0toif first.c=1 then e=0, to see if/how they change the output. Also try addingput (c d e)(=);aftere+d;
– Quentin
Nov 14 '18 at 14:10
add a comment |
1
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out theif last.c;statement and changingif first.c then e=0toif first.c=1 then e=0, to see if/how they change the output. Also try addingput (c d e)(=);aftere+d;
– Quentin
Nov 14 '18 at 14:10
1
1
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out the
if last.c; statement and changing if first.c then e=0 to if first.c=1 then e=0, to see if/how they change the output. Also try adding put (c d e)(=); after e+d;– Quentin
Nov 14 '18 at 14:10
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out the
if last.c; statement and changing if first.c then e=0 to if first.c=1 then e=0, to see if/how they change the output. Also try adding put (c d e)(=); after e+d;– Quentin
Nov 14 '18 at 14:10
add a comment |
2 Answers
2
active
oldest
votes
In SAS there are two different if statements - if-then-else and subsetting if. They have similar syntax but they do different things. You have one of each in your code.
This is how it's explained in the documentation:
The subsetting IF statement is equivalent to this IF-THEN statement:
if not (expression) then delete;
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
add a comment |
Without a THEN clause the IF statement is a subsetting statement. Basically if the condition is not true the current iteration of the data step stops and control returns to the top to process the next observation.
SAS evaluates any value that is not zero or missing as true. The automatic FIRST. and LAST. variables generated when you use a BY statement will have values of either 1 (true) or 0 (false). The FIRST. variable will be true when on the first observation for the BY group and the LAST. variable will be true when on the last observation for the BY group.
Your data step is getting the sum of the values of D for each value of C.
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
add a comment |
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2 Answers
2
active
oldest
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2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
In SAS there are two different if statements - if-then-else and subsetting if. They have similar syntax but they do different things. You have one of each in your code.
This is how it's explained in the documentation:
The subsetting IF statement is equivalent to this IF-THEN statement:
if not (expression) then delete;
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
add a comment |
In SAS there are two different if statements - if-then-else and subsetting if. They have similar syntax but they do different things. You have one of each in your code.
This is how it's explained in the documentation:
The subsetting IF statement is equivalent to this IF-THEN statement:
if not (expression) then delete;
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
add a comment |
In SAS there are two different if statements - if-then-else and subsetting if. They have similar syntax but they do different things. You have one of each in your code.
This is how it's explained in the documentation:
The subsetting IF statement is equivalent to this IF-THEN statement:
if not (expression) then delete;
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
In SAS there are two different if statements - if-then-else and subsetting if. They have similar syntax but they do different things. You have one of each in your code.
This is how it's explained in the documentation:
The subsetting IF statement is equivalent to this IF-THEN statement:
if not (expression) then delete;
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
answered Nov 14 '18 at 10:08
user667489user667489
7,93221227
7,93221227
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
add a comment |
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
Thank you, I am a beginner so a simple guidance was really all I wanted. That was very helpful.
– hyg17
Nov 14 '18 at 19:16
add a comment |
Without a THEN clause the IF statement is a subsetting statement. Basically if the condition is not true the current iteration of the data step stops and control returns to the top to process the next observation.
SAS evaluates any value that is not zero or missing as true. The automatic FIRST. and LAST. variables generated when you use a BY statement will have values of either 1 (true) or 0 (false). The FIRST. variable will be true when on the first observation for the BY group and the LAST. variable will be true when on the last observation for the BY group.
Your data step is getting the sum of the values of D for each value of C.
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
add a comment |
Without a THEN clause the IF statement is a subsetting statement. Basically if the condition is not true the current iteration of the data step stops and control returns to the top to process the next observation.
SAS evaluates any value that is not zero or missing as true. The automatic FIRST. and LAST. variables generated when you use a BY statement will have values of either 1 (true) or 0 (false). The FIRST. variable will be true when on the first observation for the BY group and the LAST. variable will be true when on the last observation for the BY group.
Your data step is getting the sum of the values of D for each value of C.
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
add a comment |
Without a THEN clause the IF statement is a subsetting statement. Basically if the condition is not true the current iteration of the data step stops and control returns to the top to process the next observation.
SAS evaluates any value that is not zero or missing as true. The automatic FIRST. and LAST. variables generated when you use a BY statement will have values of either 1 (true) or 0 (false). The FIRST. variable will be true when on the first observation for the BY group and the LAST. variable will be true when on the last observation for the BY group.
Your data step is getting the sum of the values of D for each value of C.
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
Without a THEN clause the IF statement is a subsetting statement. Basically if the condition is not true the current iteration of the data step stops and control returns to the top to process the next observation.
SAS evaluates any value that is not zero or missing as true. The automatic FIRST. and LAST. variables generated when you use a BY statement will have values of either 1 (true) or 0 (false). The FIRST. variable will be true when on the first observation for the BY group and the LAST. variable will be true when on the last observation for the BY group.
Your data step is getting the sum of the values of D for each value of C.
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
answered Nov 14 '18 at 18:54
TomTom
23.2k2718
23.2k2718
add a comment |
add a comment |
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1
Have you looked at the documentation for the IF statement? Please demonstrate that you have done some basic research before posting questions.
– user667489
Nov 13 '18 at 10:10
I understand that IF-THEN/ELSE statements can conditionally execute codes. I also know that FIRST.variable is equal to 1 when the first observation of that variable is found and 0 otherwise. It is just confusing that when there are no THEN or ELSE statements that follows. It's like saying, I evaluated if the last variable is 1 or 0, so what?
– hyg17
Nov 14 '18 at 3:13
Please add an example step that makes input dataset B, and show the output you get from your step and describe how it differs from the output you want. Once you have the example you can play with your code, trying things like commenting out the
if last.c;statement and changingif first.c then e=0toif first.c=1 then e=0, to see if/how they change the output. Also try addingput (c d e)(=);aftere+d;– Quentin
Nov 14 '18 at 14:10