Date format in SAS - r

Question

I have a SAS code that I need to convert into R.
My SAS code is something like this -
proc sql;
create table data as
select a.*,b.qty from Sales as a inner join Units as b
on a.id=b.id and put(a.date,yymmn6.)=put(c.date,yymmn6.)
quit;
I know that put(a.date,yymmn6.) converts the date into a SAS date value. But what does a.date become after this function? If date=01jan2012, put(a.date,yymmn6.) makes it as some SAS value that represents 201201 or 20120101? i.e. the SAS value created will stand for the whole date or just the year and mon of the date?
Currently, I am writing the R code for this as -
data <- sqldf("select a.*,b.qty from Sales as a inner join Units as b
on a.id=b.id and a.date=c.date")
Should I be doing it as -
Sales$date <- as.yearmon(Sales$date)
Units$date <- as.yearmon(Units$date)
data <- sqldf("select a.*,b.qty from Sales as a inner join Units as b
on a.id=b.id and a.date=c.date")
I don't have access to SAS and hence, I cannot try this out on a sample data. Any help would be great. Thanks!

Answer 1

put(a.date,yymmn6.) converts a numeric date value to a character value stored as yyyymm (e.g. 201201). Therefore the join condition is matching all dates where the month and year are the same, but not necessarily the day.
I'm not sure of the best way of achieving this in R, but you seem to have some ideas on this.
Hope this helps.

Answer 2

When you use put(a.date,yymmn6.) the output of that function is a character. Put takes a numeric input and format and outputs the formatted numeric value as character. input function does the opposite.
data mydata;
sas_numeric_date = "01jan2012"d;
sas_yyyymm_char_date = put(sas_numeric_date, yymmn6.);
sas_yyyymm_numeric_date = input(sas_yyyymm_char_date, yymmn6.);
output;
sas_numeric_date = "29Feb2012"d;
sas_yyyymm_char_date = put(sas_numeric_date, yymmn6.);
sas_yyyymm_numeric_date = input(sas_yyyymm_char_date, yymmn6.);
output;
format sas_numeric_date sas_yyyymm_numeric_date date9.;
run;
sas_numeric_date sas_yyyymm_char_date sas_yyyymm_numeric_date
01Jan2012 201201 01Jan2012
29Feb2012 201202 01Feb2012
So, when you apply the yymmn6. as informat on sas_yyyymm_char_date - which itself is in yyyymm format, the resulting value is numeric and day part in the date defaults to the first day of the month as shown above.