Generating an MD5 hash expression

This macro, mp_md5, constructs a character string that, when executed in a DATA step, calculates a composite MD5 hash for the specified variables. It is designed to be robust in the face of complex cases such as large floating-point numbers, special numeric missing values, and a large number of columns. The algorithm concatenates the MD5 hashes of each individual variable. The documentation indicates that it does not work in a PROC SQL and may cause errors if the option 'options dsoptions=nonote2err;' is active and non-special missing data exists.

Data Analysis

Type : SASHELP

The macro is designed to apply to any SAS table being processed in a DATA step. The example provided in the documentation uses the SASHELP.CLASS table, which is a standard internal SAS source. No external data is needed for the example.

1 Code Block

Macro

Explanation :
Defines the 'mp_md5' macro which takes as parameters a list of character variables (cvars) and numeric variables (nvars). The macro dynamically generates a series of SAS function calls. For each variable, it calculates an individual MD5 hash ('put(md5(...),$hex32.)'). For numeric variables, it applies a trick `ifn(missing(&var),&var,&var*1)` to preserve special missing values while correcting floating-point precision errors. All individual hashes are then concatenated (separated by '!!') and the final result is itself hashed by the MD5 function to produce a single hash key.

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1	%macro mp_md5(cvars=,nvars=);
2	%local i var sep;
3	put(md5(
4	%DO i=1 %to %sysfunc(countw(&cvars));
5	%let var=%scan(&cvars,&i,%str( ));
6	&sep put(md5(trim(&var)),$hex32.)
7	%let sep=!!;
8	%END;
9	%DO i=1 %to %sysfunc(countw(&nvars));
10	%let var=%scan(&nvars,&i,%str( ));
11	/* multiply by 1 to strip precision errors (eg 0 != 0) */
12	/* but ONLY if not missing, else will lose any special missing values */
13	&sep put(md5(trim(put(ifn(missing(&var),&var,&var*1),binary64.))),$hex32.)
14	%let sep=!!;
15	%END;
16	),$hex32.)
17	%mend mp_md5;

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