Is it necessary to use ":" for string longer than 8 characters? - sas

Question

In the following program all data is read correctly
data test ;
infile datalines ;
input make 10$ mpg ## ; /* should I use make : 10$ . . */
datalines ;
Ford 20 Honda 29 Oldsmobile 20 Cadillac 17
Toyota 24 Chevrolet 17
;
run ;
proc print ;
run ;
The above code works fine, however my teacher says that I must use colon : and the correct answer is input make : 10$ mpg ## ;
I dont understand why . As far as I know : is useful if we have trailing spaces at the begining of a record line , otherwise why should we use it here ?

Answer 1

The colon tells SAS to use the following informat. Without the colon SAS would ignore that part (it doesn't do anything). SAS by default uses an informat (and resultant length) of $8. if you don't specify it otherwise.
You are always better off specifying the informat, as a character of 2 length stored in the default 8 length character variable would be wasting storage space and processing time, but it won't alter the value (assuming you know to be aware of the trailing spaces).
You can also specify the informat ahead of time:
data test;
infile datalines;
informat make $10.;
input
make $ mpg ##;
datalines;
Ford 20 Honda 29 Oldsmobile 20 Cadillac 17
Toyota 24 Chevrolet 17
;;;;
run;
proc print data=test;
run ;
I find that usually easier to read, although using :$10. in stream is acceptable as well.

Answer 2

The : modifier on the INPUT statement says to read the text using LIST MODE even when there is an in-line format specification. In list mode the input statement reads the next word on the line into the variable. Without the : modifier the INPUT statement FORMATTED MDOE will be used which will read exactly the number of character specified by the in-line informat. Even if this could cause it to stop before the end of the current word on the line or read past the delimiter into the next word on the line.
But there are other problems with your INPUT statement. As currently written it will generate an error.
2112 input make 10$ mpg ## ;
-
22
ERROR 22-322: Expecting a name.
The number 10 in the INPUT statement is taken to mean you want to read MAKE using COLUMN MODE input. So you want to read the single digit number from the 10th character on the line. Then the $ modifier after the column number is generating an error because there is no variable directly in front of it to modify. If you want specify an informat you need to include the period as part of the specification. If you want to specify a character informat instead of a numeric informat then the name of the informat should start with the $ character.
So your INPUT statement with an in-line informat specification for MAKE would look like:
input make :$10. mpg ## ;
The other way to make sure the MAKE is defined long enough to hold 10 characters is to define the variable before referencing it in the INPUT statement. Then SAS does not have to guess how you want it defined by how you are using it in the INPUT statement. Once the variable is known there is no need to include any extra characters in the INPUT statement.
data test ;
length make $10 mpg 8;
input make mpg ## ;
datalines ;
Ford 20 Honda 29 Oldsmobile 20 Cadillac 17
Toyota 24 Chevrolet 17
;