The Confusing String in SAS

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** Things under legendu.net/outdated are outdated technologies that the author does not plan to update any more. Please look for better alternatives. **

1. the min function also works on string variables.

2. A missing character in SAS is represented by any number of white spaces. To see more detailed discussion on missing values, please refer to the post Missing Values in SAS.

3. In the data step characters and number are implicitly converted to each other when necessary. However, this is not the case in proc iml. You have to use the char function to convert number to string in the iml procedure.

the convert of dot and blank values? ... if I remember correctly, A missing character value (any number of white spaces) becomes a missing numeric value (.) when converted to numeric. However, a missing numeric value (.) becomes "." when converted to character. The inconsistent behavior here is annoying.

1. When you define a variable in SAS, it has a fixed length (no matter it is numeric or character). Things can be really tricky for (fixed length) character variables. Suppose we have a string variable s. If you concatenate s (using || or cat) with another string and assign it back to s as illustrated below

s = cat(s, "another string");

you will find that the value of s is not changed. This is caused by the fact that a string in SAS has a fixed length. The value of a string variable is always truncated/padded to meet the length requirement. When you assign cat(s, "another string") to s the concatenated part is truncated, so the value s stays the same. To avoid this problem, you should always remove leading and trailing white spaces (using strip)in string variables before concatenating them unless you know what you are doing. There is a function catx in SAS, which automatically strips string variables before concatenating them. Another tricky issue caused by this is when you convert between numeric and character values. Always strip a value/variable before you convert it to the other type.

1. The use of string in SAS is a little bit confusing. Some rules of them are summarized below.

   • You should not use single/double quotation marks in macro (i.e., outside the data step and procedures) except for numbers represented using string (e.g., '01aug11'd) or literal quotations marks. This is because that macros are essentially string. For example, you should not quote month in the following code, however, you must quote 08aug2013.

%let alertdatestr= %sysfunc(compress(%sysfunc(putn(%eval(%sysfunc(intnx(month, '08aug2013'd, 0))), YYMMDD10.)),'-'));
%put &alertdatestr;

- You have to use single/double quotation marks 
for strings (including informat/outformat) inside data steps or procedures.
However, informat/outformat (e.g., `date9.`, `datetime19.`, etc.) 
in a `put`, `%put` statement should not be quoted.
For example, 
you must quote `week` in the following code. 
However, pay attention to when `date9.` should be quoted and when not.

data _null_;
    x = intnx('week', '17oct03'd, 6);
    y = putn('17Oct2013'd, "date9.");
    put x date9.;
run;

1. The function compress removes specified characters from a string. If the character list is not specified, then spaces are removed. It is functionally equivalent to replace the specified characters with blank strings. It is similar to std::remove_if on std::string in C++.

2. The function tranwrd replaces a substring with another one. It is similar to sub/gsub in R and str.replace in Python. It takes 3 arguments; first is source string; second is string to be replaced and last one is string to be replaced by. tranwrd will find out every occurrence of the second argument in the first argument and will replace it with the third argument.

3. Do not pass numerical arguments to functions taking string arguments, and vice versa.

4. Generally speaking, you do not have to quote macros. However, when you use a macro variable in a string, you must quote it in double quotes (A macro variable in single quotes does not expand.) For example, you have to quote &dir. in the following SAS statement.

libname N3D "&dir.";

1. The function lowcase converts all letters in a string to lower case. It is similar to the function tolower in R and str.lower in Python.

2. The function upcase converts all letters in a string to upper case. It is similar to the functions toupper in R and str.upper in Python.

3. The function substr extracts a sub string from a string. The length of the sub string cannot exceedes the maximum possible length.

4. The function scan is somewhat similar to the function split in R and str.split in Python. However , it is different in the sense that it returns the nth word (from a string) instead of return a vector/list of words. You can use multiple delimiters for scan.

5. left/%left is equivalent to the function ltrim in VBA.

6. In most programming languages, you have to escape the backslash (\) in Windows paths. In SAS, it does not matter whether you escape it or not.

7. To escape the double/single quotation mark, you can double it. For example,

data _null_;
    x = 'How''s everything going?';
    put x;
    y = "What do you mean by ""BTW""?";
    put y;
run;

Tricks and Traps

1. The function trim is a different from trim functions in other programming languages. While in most programming languages trim removes both leading and trailing blanks, the trim function in SAS removes only trailing blanks. To remove both leading and trailing blanks in SAS, you have to use the function strip.

2. You cannot set the delimiter to be blank in catx. If you specify "" as the delimiter, then " " will be used. This is really really stupid.

strip/trim/compress

strip removes both trailing and leading white spaces TRIM Function Removes trailing blanks from a character string, and returns one blank if the string is missing. this is ugly as most languages, trim is strip

however, compress is much more diffrent!!! Returns a character string with specified characters removed from the original string.

you will use strip to remove .. most of the time.