formatting variables and then recoding - sas

Question

I started out formatting my variables using PROC FORMAT. Later on I found that I had to change some of my variables in my dataset. I want to maintain the formatting I originally created, but I don't think I can do this if I recode. Am I correct in assuming this? I think I will have to just change some of my formats to accommodate my new variables, but is there a way

Answer 1

I'm not quite sure I understand your question, but I think I can still answer your question by giving you an understanding of the difference between recoding variables in SAS and using formatted values.
If you have originally created a format, that format is applied to the values in the SAS dataset at the time that your analysis is run. So, if you have a value of "Block A" in a character variable in your dataset and you have formatted value that maps "Block A" to the formatted value of 1, then if you go in and later change the value of "Block A" to something else and rerun your analysis, "Block A" will not longer be printed in your output or used in your analysis as the formatted value. Formats work independently of the underlying values in your datasets. When you run an analysis SAS essentially looks through your datasets at run-time and maps each of the values to the formatted values as you've specified in your proc format statement and then performs the analysis using the formatted values.
If you want to keep the original formatting, you can use two separate formats: one for the old format and one for the new formatting and call the appropriate format into your procedures depending on when you want to use which format.
You can also use a put statement in a datastep to convert the previously formatted value and "hard code" the formatted value as an actual value in your dataset. For example, if you have a format called "blockno" that you used with a variable called "block" then, using your old format, you could create a variable called blockno_old and set it to the old formatted value with:
block_old=put(block, $blockno.).
You could then modify block with your new values. You would then have to variables in your dataset: block_old which would contain the original values of your variable and block which, after your changes, would contain the new values.

Answer 2

Proc Format is not a format statement
With proc format, you create formats, you do not assign them to variables. That you can do for instance with a format statement.
The format of a variable is not its internal length
A SAS variable can only have two types: numerical (which non SAS programmers call double) or chracter (which non SAS programmers call fixed length character) It can however have hundreds of different formats. The format just determines the way the variable is represented in a report.
You can perfectly change the format of a variable without changing it's length.
Try this:
proc format;
value myFormat
0-10 = 'small'
10-20 ='medium'
20-100='large' ;
run;
data test1;
infile datalines;
length myVar 8.;
input myVar;
format myVar 6.2;
datalines;
1
2.1
9.12
10.123
15.1234
22.12345
50.123456
;
data test2;
set test1;
format myVar myFormat.;
data test3;
set test2;
format myVar 12.6;
run;
title 'In test1, myVar has format 6.2';
proc print data=test1;
run;
title 'In test2, myVar has format myFormat';
proc print data=test2;
run;
title 'In test3, myVar has format 12.6';
proc print data=test3;
run;

Answer 3

You can create a format in a format catalog and store it for any future reference. It always happens that the dataset has new variables and updated variables with new data. So having a format catalog to accommodate the new and old changes will actually help to maintain history of the original and current values.