Macro AHGkeepN - Sequential filtering by group

The `AHGkeepN` macro filters a dataset to keep only the first N observations (or a range defined by m and n) for each unique combination of variables specified in the `by` parameter. It first sorts the data, then uses an internal counter within a Data Step to select the desired rows. It appears to depend on external utility macros (`%AHGblank`, `%AHGbarename`, `%AHGcount`) not defined in this script.

Data Analysis

Type : EXTERNAL

The dataset is dynamically specified via the `dsn` parameter when calling the macro.

1 Code Block

PROC SORT Data

Explanation :
Sorts the input table (`dsn`) according to the grouping variables (`by`) and stores the result in the output table (`out`). If `out` is not specified, a name is derived from `dsn`.

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1	%IF %AHGblank(&out) %THEN %let out=%AHGbarename(&dsn);
2	PROC SORT DATA=&dsn out=&out;
3	BY &BY;
4	RUN;

2 Code Block

DATA STEP Data

Explanation :
Reads the sorted table and uses a temporary counter (`ahuigeID3498273456`) to number observations within each group defined by the last variable in the `by` list. Only observations whose rank is strictly greater than `m` and less than or equal to `n` are retained.

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1	DATA &out(drop=ahuigeID3498273456);
2	SET &out;
3	BY &BY;
4	IF first.%scan(&BY,%AHGcount(&BY)) THEN ahuigeID3498273456=1;
5	ELSE ahuigeID3498273456+1;
6	IF &mTHEN OUTPUT;
7	RUN;

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