I have been trying to execute a sas code using arrays. Strangely, it is not working the way i was expecting. So i used another approach and code runs fine with second method. But still i want to know ehat is wrong with the first method. Following is my code:
data have;
input free_m prevention substitution oth;
datalines;
. . . .
. 0 0 0
1 1 0 0
;
run;
data test;
set have;
/*method1*/
array a1(*) prevention substitution oth;
do i=1 to dim(a1);
if free_m=. and prevention=0 and substitution=0 and oth=0 then a1(i)=.;
end;
/*method2*/
/*
if free_m=. and prevention=0 and substitution=0 and oth=0 then
do;
prevention=.;
substitution=.;
oth=.;
end;
*/
drop i;
run;
proc sql;
select * from test;
quit;
The outcome with /method2/ is correct and it is what i want:
But with /method1/, i am getting following output:
Is there anything wrong in method1? Kindly help!
Thanks a lot.
You are cutting off the limb that you are sitting on.
The first method works fine for I=1 and I=2 but when you get to I=3 and I=4 the values of prevention has been change from 0 to missing by the earlier iterations of the do loop. prevention and a1(2) refer to the same thing.
Related
I'm coming at SAS from a Python/R/Stata background, and learning that things are rather different in SAS. I'm approaching the following problem from the standpoint of one of these languages, perhaps SAS isn't up to what I want to do.
I have a panel dataset with an age column in it. I want to add new columns to the dataset using this age column. I'm going to simplify the functions of age to keep it simple in my example.
The goal is to loop over a sequence, and use the value of that sequence at each loop step to 1. assign the name of the new column and 2. assign the values of that column. I'm hoping to get my starting dataset, with new columns added to it taking values spline1 spline2... spline7
data somePath.FinalDataset;
do i = 1 to 7;
if i = 1 then
spline&i. = age;
if i ^= 1 then spline&i. = age + i;
end;
set somePath.StartingDataset;
run;
This code won't even run, though in an earlier version I was able to get it to run, but the new columns had their values shifted down one row from what they should have been. I include this code block as pseudocode of what I'm trying to do. Any help is much appreciated
One way to do this in SAS is with arrays. A SAS array can be used to reference a group of variables, and it can also create variables.
data have;
input age;
cards;
5
10
;
run;
data want;
set have;
array spline{7}; *create spline1 spline2 ... spline7;
do i=1 to 7;
if i = 1 then spline{i} = age;
else spline{i} = age + i;
end;
drop i;
run;
Spline{i} referes to the ith variable of the array named spline.
i is a regular variable, the DROP statement prevents it from being written to the output dataset.
When you say new columns were "shifted by one," note that spline1=age and spline2=age+2. You can change your code accordingly, e.g. if you want spline2=age+1, you could change your else statement to else spline{i} = age + i - 1 ; It is also possible to change the array statement to define it with 0 as the lower bound, rather than 1.
Arrays are likely the best way to solve this, but I will demonstrate a macro approach, which is necessary in some cases.
SAS separates its doing-things-with-data language from its writing-code language into the 'data step language' and the 'macro language'. They don't really talk to each other during a data step, because the macro language runs during the compilation stage (before any data is processed) while the data step language runs during the execution stage (while rows of data are being processed).
In any event, for something like this it's quite possible to write a macro to do what you want. Borrowing Quentin's general structure and initial dataset:
data have;
input age;
cards;
5
10
;
run;
%macro make_spline(var=, count=);
%local i;
%do i = 1 %to &count;
%if &i=1 %then &var.&i. = &var.;
%else &var.&i. = &var. + &i.;
; *this semicolon ends the assignment statement;
%end;
/* You end up with the IF statement generating:
age1 = age
and the extra semicolon after the if/else generates the ; for that line, making it
age1 = age;
etc. for the other lines.
*/
%mend make_spline;
data want;
set have;
%make_spline(var=age,count=7);
run;
This would then perform what you're looking to perform. The looping is in the macro language, not in the data step. You can assign parameters however you see fit; I prefer to have parameters like above, or even more (start loop could also be a parameter, and in fact the assignment code could be a parameter!).
Suppose the dataset has 3 columns
Obs Theo Cal
1 20 20
2 21 23
3 21 .
4 22 .
5 21 .
6 23 .
Theo is the theoretical value while Cal is the estimated value.
I need to calculate the missing Cal.
For each Obs, its Cal is a linear combination of previous two Cal values.
Cal(3) = Cal(2) * &coef1 + Cal(1) * &coef2.
Cal(4) = Cal(3) * &coef1 + Cal(2) * &coef2.
But Cal = lag1(Cal) * &coef1 + lag2(Cal) * &coef2 didn't work as I expected.
The problem with using lag is when you use lag1(Cal) you're not getting the last value of Cal that was written to the output dataset, you're getting the last value that was passed to the lag1 function.
It would probably be easier to use a retain as follows:
data want(drop=Cal_l:);
set have;
retain Cal_l1 Cal_l2;
if missing(Cal) then Cal = Cal_l1 * &coef1 + Cal_l2 * &coef2;
Cal_l2 = Cal_l1;
Cal_l1 = Cal;
run;
I would guess you wrote a datastep like so.
data want;
set have;
if missing(cal) then
cal = lag1(cal)*&coef1 + lag2(cal)*&coef2;
run;
LAG isn't grabbing a previous value, but is rather creating a queue that is N long and gives you the end piece of. If you have it behind an IF statement, then you will never put the useful values of CAL into that queue - you'll only be tossing missings into it. See it like so:
data have;
do x=1 to 10;
output;
end;
run;
data want;
set have;
real_lagx = lag(x);
if mod(x,2)=0 then do;
not_lagx = lag(x);
put real_lagx= not_lagx=;
end;
run;
The Real lags are the immediate last value, while the NOT lags are the last even value, because they're inside the IF.
You have two major options here. Use RETAIN to keep track of the last two observations, or use LAG like I did above before the IF statement and then use the lagged values inside the IF statement. There's nothing inherently better or worse with either method; LAG works for what it does as long as you understand it well. RETAIN is often considered 'safer' because it's harder to screw up; it's also easier to watch what you're doing.
data want;
set have;
retain cal1 cal2;
if missing(cal) then cal=cal1*&coef1+cal2*&coef2;
output;
cal2=cal1;
cal1=cal;
run;
or
data want;
set have;
cal1=lag1(cal);
cal2=lag2(cal);
if missing(cal) then cal=cal1*&coef1+cal2*&coef2;
run;
The latter method will only work if cal is infrequently missing - specifically, if it's never missing more than once from any three observations. In the initial example, the first cal (row 3) will be populated, but from there on out it will always be missing. This may or may not be desired; if it's not, use retain.
There might be a way to accomplish it in a DATA step but as for me, when I want SAS to process iteratively, I use PROC IML and a do loop. I named your table SO and succesfully ran the following :
PROC IML;
use SO; /* create a matrix from your table to be used in proc iml */
read all var _all_ into table;
close SO;
Cal=table[,3];
do i=3 to nrow(cal); /* process iteratively the calculations */
if cal[i]=. then do;cal[i]=&coef1.*cal[i-1]+&coef2.*cal[i-2];
end;else do;end;
end;
table[,3]=cal;
Varnames={"Obs" "Theo" "Cal"};
create SO_ok from table [colname=varnames]; /* outputs a new table */
append from table;
close SO_ok;
QUIT;
I'm not saying you couldn't use lag() and a DATA step to achieve what you want to do. But I find that PROC IML is useful and more intuitive when it comes to iterative process.
I am an intermediate user of SAS, but I have limited knowledge of arrays and macros. I have a set of code that prompts the user to enter a date range. For example, the user might enter December 1, 2015-December 5,2015. For simplicity, imagine the code looks like:
data new; set old;
if x1='December 1, 2015'd then y="TRUE";
run;
I need to run this same code for every day in the date prompt range, so for the 1st, 2nd, 3rd, 4th, and 5th. My thought was to create an array that contains the dates, but I am not sure how I would do that. My second thought was to create a macro, but I can't figure out out to feed a list through a macro.
Also, just FYI, the code is a lot longer and more complicated than just a data step.
The following macro can be used as a framework for your code:
%MACRO test(startDate, endDAte);
%DO i=&startDate %to &endate;
/* data steps go here */
/* example */
DATA test;
SET table;
IF x1 = &i THEN y = "true";
RUN;
%END;
%MEND;
Look into call execute to call your macro and a data null step using a do loop to loop through the days. Getting the string correct for the call execute can sometimes be tricky, but worth the effort overall.
data sample;
do date='01Jan2014'd to '31Jan2014'd;
output;
end;
run;
%macro print_date(date);
proc print data=sample;
where date="&date"d;
format date date9.;
run;
%mend;
%let date_start=05Jan2014;
%let date_end=11Jan2014;
data _null_;
do date1="&date_start"d to "&date_end"d by 1;
str='%print_date('||put(date1, date9.)||');';
call execute(str);
end;
run;
I cannot seem to find a way to use and if-then or just an if statement below the unique command in the SAS merge code below. I am matching all of the same S2_Liab numbers just pulling a different number where there is a different title in the "Liability_Lmt" column.
/*--------------------------------------------------------------------------------------
/*---- Additional Partner and/or Corporation charge ----------
/*--------------------------------------------------------------------------------------
data full;
set whole_FR;
record_num=_N_;
S2_Liab = S2LiabLimit;
run;
proc sort;
by S2_Liab;
run;
data unique(keep=S2_Liab S2Partners P_charge FD_charge);
set WORK.FR_S2_Mandatory_Liab_Cov;
S2_Liab = Liability_Lmt;
if Additional = "Partner_Corp" then P_charge = round(&thestate.,0.01);
if Additional = "Farm_Dwelling" then FD_charge = round(&thestate.,0.01);
run;
proc sort nodupkey;
by S2_Liab;
run;
data match nonmatch;
merge full(in=a) unique(in=b);
by S2_Liab;
if a=1 and b=1 then output match;
if a=1 and b=0 then output nonmatch;
run;
data whole_FR;
set match nonmatch;
proc sort;
by record_num;
run;
For the first if-then statement above I am getting no results, instead the code seems to skip directly to the second if-then statement.
These are my results show me all of the numbers for the second if statement ("FD_charge") but blank answers for "P_charge". For some reason the program skips over the first if statement and prints out the answer for the second if statement. I have also tried an if-then-else statement but I get the same answers.
Does anybody have a clue how to make this work?
Hi another quick question
in proc sql we have on which is used for conditional join is there something similar for sas data step
for example
proc sql;
....
data1 left join data2
on first<value<last
quit;
can we replicate this in sas datastep
like
data work.combined
set data1(in=a) data2(in=b)
if a then output;
run;
You can also can reproduce sql join in one DATA-step using hash objects. It can be really fast but depends on the size of RAM of your machine since this method loads one table into memory. So the more RAM - the larger dataset you can wrap into hash. This method is particularly effective for look-ups in relatively small reference table.
data have1;
input first last;
datalines;
1 3
4 7
6 9
;
run;
data have2;
input value;
datalines;
2
5
6
7
;
run;
data want;
if _N_=1 then do;
if 0 then set have2;
declare hash h(dataset:'have2');
h.defineKey('value');
h.defineData('value');
h.defineDone();
declare hiter hi('h');
end;
set have1;
rc=hi.first();
do while(rc=0);
if first<value<last then output;
rc=hi.next();
end;
drop rc;
run;
The result:
value first last
2 1 3
5 4 7
6 4 7
7 6 9
Yes there is a simple (but subtle) way in just 7 lines of code.
What you intend to achieve is intrinsically a conditional Cartesian join which can be done by a do-looped set statement. The following code use the test dataset from Dmitry and a modified version of the code in the appendix of SUGI Paper 249-30
data data1;
input first last;
datalines;
1 3
4 7
6 9
;
run;
data data2;
input value;
datalines;
2
5
6
7
;
run;
/***** by data step looped SET *****/
DATA CART_data;
SET data1;
DO i=1 TO NN; /*NN can be referenced before set*/
SET data2 point=i nobs=NN; /*point=i - random access*/
if first<value<last then OUTPUT; /*conditional output*/
END;
RUN;
/***** by SQL *****/
proc sql;
create table cart_SQL as
select * from data1
left join data2
on first<value<last;
quit;
One can easily see that the results coincide.
Also note that from SAS 9.2 documentation: "At compilation time, SAS reads the descriptor portion of each data set and assigns the value of the NOBS= variable automatically. Thus, you CAN refer to the NOBS= variable BEFORE the SET statement. The variable is available in the DATA step but is not added to any output data set."
There isn't a direct way to do this with a MERGE. This is one example where the SQL method is clearly superior to any SAS data step methods, as anything you do will take much more code and possibly more time.
However, depending on the data, it's possible a few approaches may make sense. In particular, the format merge.
If data1 is fairly small (even, say, millions of records), you can make a format out of it. Like so:
data fmt_set;
set data1;
format label $8.;
start=first; *set up the names correctly;
end=last;
label='MATCH';
fmtname='DATA1F';
output;
if _n_=1 then do; *put out a hlo='o' line which is for unmatched lines;
start=.; *both unnecessary but nice for clarity;
end=.;
label='NOMATCH';
hlo='o';
output;
end;
run;
proc format cntlin=fmt_set; *import the dataset;
quit;
data want;
set data2;
if put(value,DATA1F.)="MATCH";
run;
This is very fast to run, unless data1 is extremely large (hundreds of millions of rows, on my system) - faster than a data step merge, if you include sort time, since this doesn't require a sort. One major limitation is that this will only give you one row per data2 row; if that is what is desired, then this will work. If you want repeats of data2 then you can't do it this way.
If data1 may have overlapping rows (ie, two rows where start/end overlap each other), you also will need to address this, since start/end aren't allowed to overlap normally. You can set hlo="m" for every row, and "om" for the non-match row, or you can resolve the overlaps.
I'd still do the sql join, however, since it's much shorter to code and much easier to read, unless you have performance issues, or it doesn't work the way you want it to.
Here's another solution, using a temporary array to hold the lookup dataset. Performance is probably similar to Dmitry's hash-based solution, but this should also work for people still using versions of SAS prior to 9.1 (i.e. when hash objects were first introduced).
I've reused Dmitry's sample datasets:
data have1;
input first last;
datalines;
1 3
4 7
6 9
;
run;
data have2;
input value;
datalines;
2
5
6
7
;
run;
/*We need a macro var with the number of obs in the lookup dataset*/
/*This is so we can specify the dimension for the array to hold it*/
data _null_;
if 0 then set have2 nobs = nobs;
call symput('have2_nobs',put(nobs,8.));
stop;
run;
data want_temparray;
array v{&have2_nobs} _temporary_;
do _n_ = 1 to &have2_nobs;
set have2 (rename=(value=value_array));
v{_n_}=value_array;
end;
do _n_ = 1 by 1 until (eof_have1);
set have1 end = eof_have1;
value=.;
do i=1 to &have2_nobs;
if first < v{i} < last then do;
value=v{i};
output;
end;
end;
if missing(value) then output;
end;
drop i value_array;
run;
Output:
value first last
2 1 3
5 4 7
6 4 7
7 6 9
This matches the output from the equivalent SQL:
proc sql;
create table want_sql as
select * from
have1 left join have2
on first<value<last
;
quit;
run;