Calcite | Level 5

## how to fill up a dataset with samples till a certain sample size is reached ?

Hi,

I have two data sets a and b with 200 entries each.  While we have the capacity to test 350 samples each month, I have to use one of the data sets each month (in alternating mode so a b a b etc), and top the remaining places up with samples from the other dataset.

So say, for January, I use dataset a and top it up with 150 samples of dataset b.

In this case I could simply use Proc Sql... obs = 150

However, the samples set sizes change every month.

What do I need to do to :

choose a and fill up samples from sample set b till samples size = 350.

Any ideas are highly welcome.

Many thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Opal | Level 21

## Re: how to fill up a dataset with samples till a certain sample size is reached ?

@Anna_NZ

Here one way to go:

``````data have_a;
ds='A';
do i=1 to 200;
output;
end;
run;

data have_b;
ds='B';
do i=1 to 200;
output;
end;
run;

%let n_sample=350;
%let ds_all=have_a;
%let ds_sample=have_b;

data want(drop=_:);

/* ds with all records */
do while(not last_A);
set &ds_all nobs=nobs_A end=last_A;
output;
end;

/*  Method 3: Using SAS DATA Step with no sort required  */

/* Initialize _K to the number of sample obs needed and _N to the */
/*  total number of obs in the data set.                          */
_k= &n_sample - nobs_A;
_n=nobs_A;

do while(1);

set &ds_sample;

/* To randomly select the first observation for the sample, use the */
/* fact that each obs in the data set has an equal chance of being  */
/* selected: k/n. If a random number between 0 and 1 is less than   */
/* or equal to k/n, we select that the first obs for our sample     */
/* and also adjust k and the number of obs needed to complete the   */
/* sample.                                                          */

if ranuni(0) <= _k/_n then
do;
output;
_k=_k-1;
end;

/* At every iteration, adjust N, the number of obs left to */
/* sample from.                                            */
_n=_n-1;

/* Once the desired number of sample points are taken, stop iterating */
if _k=0 then leave;

end;

stop;

run;
``````
2 REPLIES 2
Opal | Level 21

## Re: how to fill up a dataset with samples till a certain sample size is reached ?

@Anna_NZ

Here one way to go:

``````data have_a;
ds='A';
do i=1 to 200;
output;
end;
run;

data have_b;
ds='B';
do i=1 to 200;
output;
end;
run;

%let n_sample=350;
%let ds_all=have_a;
%let ds_sample=have_b;

data want(drop=_:);

/* ds with all records */
do while(not last_A);
set &ds_all nobs=nobs_A end=last_A;
output;
end;

/*  Method 3: Using SAS DATA Step with no sort required  */

/* Initialize _K to the number of sample obs needed and _N to the */
/*  total number of obs in the data set.                          */
_k= &n_sample - nobs_A;
_n=nobs_A;

do while(1);

set &ds_sample;

/* To randomly select the first observation for the sample, use the */
/* fact that each obs in the data set has an equal chance of being  */
/* selected: k/n. If a random number between 0 and 1 is less than   */
/* or equal to k/n, we select that the first obs for our sample     */
/* and also adjust k and the number of obs needed to complete the   */
/* sample.                                                          */

if ranuni(0) <= _k/_n then
do;
output;
_k=_k-1;
end;

/* At every iteration, adjust N, the number of obs left to */
/* sample from.                                            */
_n=_n-1;

/* Once the desired number of sample points are taken, stop iterating */
if _k=0 then leave;

end;

stop;

run;
``````
Super User

## Re: how to fill up a dataset with samples till a certain sample size is reached ?

Grab the number of records in each table. Subtract them and create a macro variable with that value, then use that in your SQL code.

Here’s some ways to get those numbers
http://www.sascommunity.org/wiki/Determining_the_number_of_observations_in_a_SAS_data_set_efficientl...

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