In this data step I do not understand what if last.y do...
Could you tell me ?
data stop2;
set stop2;
by x y z t;
if last.y; /*WHAT DOES THIS DO ??*/
if t ne 999999 then
t=t+1;
else do;
t=0;
z=z+1;
end;
run;
LAST.Y refers to the row immediately before a change in the value of Y. So, in the following dataset:
data have;
input x y z;
datalines
1 1 1
1 1 2
1 1 3
1 2 1
1 2 2
1 2 3
1 3 1
1 3 2
1 3 3
2 3 1
2 3 2
2 3 3
;;;;
run;
LAST.Y would occur on the third, sixth, ninth, and twelfth rows in that dataset (on each row where Z=3). The first two times are when Y is about to change from 1 to 2, and when it is about to change from 2 to 3. The third time is when X is about to change - LAST.Y triggers when Y is about to change or when any variable before it in the BY list changes. Finally, the last row in the dataset is always LAST.(whatever).
In the specific dataset above, the subsetting if means you only take the last row for each group of Ys. In this code:
data want;
set have;
by x y z;
if last.y;
run;
You would end up with the following dataset:
data want;
input x y z;
datalines;
1 1 3
1 2 3
1 3 3
2 3 3
;;;;
run;
at the end.
One thing you can do if you want to see how FIRST and LAST operate is to use PUT _ALL_;. For example:
data want;
set have;
by x y z;
put _all_;
if last.y;
run;
It will show you all of the variables, including FIRST.(whatever) and LAST.(whatever) on the dataset. (FIRST.Y and LAST.Y are actually variables.)
In SAS, first. and last. are variables created implicitly within a data step.
Each variable will have a first. and a last. corresponding to each record in the DATA step. These values will be wither 0 or 1. last.y is same as saying if last.y = 1.
Please refer here for further info.
That is an example of subsetting IF statement. Which is different than an IF/THEN statement. It basically means that if the condition is not true then stop this iteration of the data step right now.
So
if last.y;
is equivalent to
if not last.y then delete;
or
if not last.y then return;
or
if last.y then do;
... rest of the data step before the run ...
end;
Related
I have a dataset that contains an ID and some additional data. I want to perform transformations based on the ID with a by statement. The transformation works. Unfortunately SAS automatically reduces the dataset to one row per group. Does anybody know how to keep the original (number of) rows and still perform the group actions?
Here is some sample code to illustrate my problem
data dat;
input ID X $;
datalines;
1 a
1 b
1 c
1 d
2 a
2 b
3 a
4 k
5 z
5 a
5 c
;
data dat_new;
length x_new $2100.;
do until(last.ID);
set dat;
by ID notsorted;
x_new = ',' ||catx(',',x,x_new);
end;
drop x;
run;
Just add an OUTPUT statement inside the DO loop.
data dat_new;
length x_new $2100.;
do until(last.ID);
set dat;
by ID notsorted;
x_new = ',' ||catx(',',x,x_new);
output;
end;
drop x;
run;
When you do not have an explicit OUTPUT statement in a data step then an implied OUTPUT statement executes at the end of the data step. Your DO loop around the SET statement means that the end of the data step is only reached for the last observation per group.
If you want the final calculated value to be replicated on each observation then just add another loop to re-read the observations and put the OUTPUT statement in that loop.
data dat_new;
length x_new $2100.;
do until(last.ID);
set dat;
by ID notsorted;
x_new = ',' ||catx(',',x,x_new);
end;
do until(last.ID);
set dat;
by ID notsorted;
output;
end;
drop x;
run;
When you want to associate a group level computation result to EACH row in the group you will need to first iterate over the group to compute the result, and then have a second loop that reads the same rows of the group and outputs each. Use additional variables if you need to know the sequence number within the group and the total number of rows in the group.
data want(keep=id x_csv_list by_group_size seq);
length x_csv_list $2100.;
do by_group_size = 1 by 1 until(last.ID);
set dat;
by ID notsorted;
x_csv_list = catx(',',x_csv_list,x);
end;
do seq = 1 to by_group_size;
set dat;
output;
end;
run;
Also, if you are at the 'never really get it' stage, remember NOTSORTED means contiguous rows with the same by group variable values.
by s
s group first.s last.s
- ----- ------- ------
A 1st 1 0
A 1st 0 0 /* trick knowledge both 0 means row is interior */
A 1st 0 1
B 2nd 1 1 /* trick knowledge both 1 means group size is 1 row */
A 3rd 1 0
A 3rd 0 1
B 4th 1 0
B 4th 0 0
B 4th 0 1
C 5th 1 0
C 5th 0 1
I don't know how to describe this question but here is an example. I have an initial dataset looks like this:
input first second $3.;
cards;
1 A
1 B
1 C
1 D
2 E
2 F
3 S
3 A
4 C
5 Y
6 II
6 UU
6 OO
6 N
7 G
7 H
...
;
I want an output dataset like this:
input first second $;
cards;
1 "A,B,C,D"
2 "E,F"
3 "S,A"
4 "C"
5 "Y"
6 "II,UU,OO,N"
7 "G,H"
...
;
Both tables will have two columns. Unique value of range of the column "first" could be 1 to any number.
Can someone help me ?
something like below
proc sort data=have;
by first second;
run;
data want(rename=(b=second));
length new_second $50.;
do until(last.first);
set have;
by first second ;
new_second =catx(',', new_second, second);
b=quote(strip(new_second));
end;
drop second new_second;
run;
output is
first second
1 "A,B,C,D"
2 "E,F"
3 "A,S"
4 "C"
5 "Y"
6 "II,N,OO,UU"
7 "G,H"
You can use by-group processing and the retain function to achieve this.
Create a sample dataset:
data have;
input id value $3.;
cards;
1 A
1 B
1 C
1 D
2 E
2 F
3 S
3 A
4 C
5 Y
6 II
6 UU
6 OO
6 N
7 G
7 H
;
run;
First ensure that your dataset is sorted by your id variable:
proc sort data=have;
by id;
run;
Then use the first. and last. notation to identify when the id variable is changing or about to change. The retain statement tells the datastep to keep the value within concatenated_value over observations rather than resetting it to a blank value. Use the quote() function to apply the " chars around the result before outputting the record. Use the cats() function to perform the actual concatenation and separate the records with a ,.
data want;
length contatenated_value $500.;
set have;
by id;
retain contatenated_value ;
if first.id then do;
contatenated_value = '';
end;
contatenated_value = catx(',', contatenated_value, value);
if last.id then do;
contatenated_value = quote(cats(contatenated_value));
output;
end;
drop value;
run;
Output:
contatenated_
value id
"A,B,C,D" 1
"E,F" 2
"S,A" 3
"C" 4
"Y" 5
"II,UU,OO,N" 6
"G,H" 7
I hope this is not a duplicate question. I've searched the forum and retain function seems to be choice of weapon but it copies down an observation, and I'm trying to do the following; for a given id, copy the second line to the first line for the x value. also first value of x is always 2.
Here's my data;
id x
3 2
3 1
3 1
2 2
2 1
2 1
6 2
6 0
6 0
and i want it to look like this;
id x
3 1
3 1
3 1
2 1
2 1
2 1
6 0
6 0
6 0
and here's the starter code;
data have;
input id x;
cards;
3 2
3 1
3 1
2 2
2 1
2 1
6 2
6 0
6 0
;
run;
Lead is tricky in SAS. You can sort in reverse and use a lag function to get around it though, and you are right: a retain statement will allow us to add an order variable so we can sort it back to its original format.
data have;
set have;
retain order;
lagid = lag(id);
if id ne lagid then order = 0;
order = order + 1;
drop lagid;
run;
proc sort data=have; by id descending order; run;
data have;
set have;
leadx = lag(x);
run;
proc sort data=have; by id order; run;
data have;
set have;
if order = 3 then x_fixed = x;
else x_fixed = leadx;
run;
If your data is exactly as you say, then you can use a lookahead merge. It literally takes the dataset and merges itself to a copy of the dataset that starts on row 2, side-to-side. You just have to check that you're still on the same ID. This does change the value of x for all records to the value one hence, not just the first; you could add additional code to pay attention to that (but can't use FIRST and LAST).
data want;
merge have have(firstobs=2 rename=(id=newid x=newx));
if newid=id then x=newx;
keep x id;
run;
If you don't have any additional variables of interest, then you can do something even more interesting: duplicate the second row in its entirety and delete the first row.
data want;
set have;
by id notsorted;
if first.id then do;
firstrow+1;
delete;
end;
if firstrow=1 then do;
firstrow=0;
output;
end;
output;
run;
However, the "safest" method (in terms of doing most likely what you want precisely) is the following, which is a DoW loop.
data want;
idcounter=0;
do _n_ = 1 by 1 until (last.id);
set have;
by id notsorted;
idcounter+1;
if idcounter=2 then second_x = x;
end;
do _n_=1 by 1 until (last.id);
set have;
by id notsorted;
if first.id then x=second_x;
output;
end;
run;
This identifies the second x in the first loop, for that BY group, then in the second loop sets it to the correct value for row 1 and outputs.
In both of the latter examples I assume your data is organized by ID but not truly sorted (like your initial example is). If it's not organized by ID, you need to perform a sort first (but then can remove the NOTSORTED).
How to add new observation to already created dataset in SAS ? For example, if I have dataset 'dataX' with variable 'x' and 'y' and I want to add new observation which is multiplication by two of the
of the observation number n, how can I do it ?
dataX :
x y
1 1
1 21
2 3
I want to create :
dataX :
x y
1 1
1 21
2 3
10 210
where observation number four is multiplication by ten of observation number two.
data X;
input x y;
datalines;
1 1
1 21
2 3
;
run;
data X ;
set X end=eof;
if eof then do;
output;
x=10 ;y=210;
end;
output;
run;
Here is one way to do this:
data dataX;
input x y;
datalines;
1 1
1 21
2 3
run;
/* Create a new observation into temp data set */
data _addRec;
set dataX(firstobs=2); /* Get observation 2 */
x = x * 10; /* Multiply each by 10 */
y = y * 10;
output; /* Output new observation */
stop;
run;
/* Add new obs to original data set */
proc append base=dataX data=_addRec;
run;
/* Delete the temp data set (to be safe) */
proc delete data=_addRec;
run;
data a ;
do kk=1 to 5 ;
output ;
end ;
run;
data a2 ;
kk=999 ;
output ;
run;
data a; set a a2 ;run ;
proc print data=a ;run ;
Result:
The SAS System 1
OBS kk
1 1
2 2
3 3
4 4
5 5
6 999
You can use macro to obtain your desired result :
Write a macro which will read first DataSet and when _n_=2 it will multiply x and y with 10.
After that create another DataSet which will hold only your muliplied value let say x'=10x and y'=10y.
Pass both DataSet in another macro which will set the original datset and newly created dataset.
Logic is you have to create another dataset with value 10x and 10y and after that set wih previous dataset.
I hope this will help !
Maybe a stupid question...
I got following dataset:
id count
x 1
y 2
z 3
a 1
b 2
c 3
etc.
And i want this:
id count group
x 1 1
y 2 1
z 3 1
a 1 2
b 2 2
c 3 2
etc.
Here is what I try:
data macro_1; set vix.macro_spy; where macro=1;
count+1;
if count>3 then do;
count=1;
end;
group=0;
if count=1 then group+1;
run;
But it is not working. How can I add all 'group' by one if I once get a 'count=1'?
Thanks.
even simpler
data want;
set vix.macro_spy;
group+(count=1);
run;
I'm not sure I understand what you need. So you have this dataset ordered so that values of variable count always go 1, 2, 3, 1, 2, 3, 1, 2, 3...
Now, you want to generate variable group so that value increments every time variable count passes over 3?
If so, you could do something like this:
data group;
set vix.macro_spy;
retain group;
if _N_ = 1 then group = 0;
if count = 1 then group + 1;
run;
This is the general pattern that I'm using.
if _N_ = 1 part is executed only once, this is where you initialize you variables.
retain statement ensures that the variable will retain its value from one iteration of the DATA step to the next.