Use the LENGTH statement to pre-set the lengths of character variables in SAS – with a comparison to R

By Eric Cai – The Chemical Statistician

(This article was first published on R programming – The Chemical Statistician, and kindly contributed to R-bloggers)

I often create character variables (i.e. variables with strings of text as their values) in SAS, and they sometimes don’t render as expected. Here is an example involving the built-in data set SASHELP.CLASS.

Here is the code:

data c1;
     set sashelp.class;
 
     * define a new character variable to classify someone as tall or short;
     if height > 60
     then height_class = 'Tall';
          else height_class = 'Short';
run;


* print the results for the first 5 rows;
proc print
     data = c1 (obs = 5);
run;

Here is the result:

Obs Name Sex Age Height Weight height_class
1 Alfred M 14 69.0 112.5 Tall
2 Alice F 13 56.5 84.0 Shor
3 Barbara F 13 65.3 98.0 Tall
4 Carol F 14 62.8 102.5 Tall
5 Henry M 14 63.5 102.5 Tall

What happened? Why does the word “Short” render as “Shor”?

This occurred because SAS sets the length of a new character variable as the length of the first value given in its definition. My code defined “height_class” by setting the value “Tall” first, which has a length of 4. Thus, “height_class” was defined as a character variable with a length of 4. Any subsequent values must follow this variable type and format.

How can we circumvent this? You can pre-set the length of any new variable with the LENGTH statement before the SET statement. In the revised code below, I correct the problem by setting the length of “height_class” to 5 before defining its possible values.

data c2;
     set sashelp.class;
 
     * define a new character variable to classify someone as tall or short;
     length height_class $ 5;
     if height > 60
     then height_class = 'Tall';
          else height_class = 'Short';
run;


* print the results for the first 5 rows;
proc print
     data = c2 (obs = 5);
run;

Here is the result:

Obs Name Sex Age Height Weight height_class
1 Alfred M 14 69.0 112.5 Tall
2 Alice F 13 56.5 84.0 Short
3 Barbara F 13 65.3 98.0 Tall
4 Carol F 14 62.8 102.5 Tall
5 Henry M 14 63.5 102.5 Tall

Notice that “height_class” for Alice is “Short”, as it should be.

An alternative solution is to re-write the code so that the first instance of “height_class” is the longest possible value. This does not require the use of the LENGTH statement.

data c3;
     set sashelp.class;
 
     * define a new character variable to classify someone as tall or short;
     if height 

By the way, I don't notice this problem in R. Here is some code to illustrate this observation.

> set.seed(235)
> 
> # randomly generate 4 values
> x = rnorm(3, 60, 5)
> 
> # add a value to the beginning of "x" so that the first value is above 60
> # add a value to the end of "x" so that the last vlaue is below 60
> x = c(63, x, 57)
> x
[1] 63.00000 70.68902 61.36082 56.62601 57.00000
> 
> # pre-allocate a vector for classifying "x" as "tall" or "short"
> y = 0 * x
> 
> 
> for (i in 1:length(x))
+ {
+   if (x[i] > 60)
+     {
+     y[i] = 'Tall'
+   }
+   else
+ {
+     y[i] = 'Short'
+   }
+ }
> 
> 
> # display "y"
> y
[1] "Tall"  "Tall"  "Tall"  "Short" "Short"

Notice that the value “Short” renders fully with a length of 5. I did not need to pre-set the length of “y” first.

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