Question
Answer and Explanation
When using SAS infile to read data from an external file, encountering a missing letter in a character column can lead to misaligned data and incorrect parsing. Here's how to handle this situation effectively:
Understanding the Problem:
The infile statement in SAS, by default, reads data based on positional formatting or delimited specifications. If a character is missing, it shifts the reading position, which can cause data from one column to be read into another. This is especially problematic with fixed-width data formats.
Solutions:
1. Using the `MISSOVER` option:
The MISSOVER option, when used in the infile statement, instructs SAS to treat missing data in the input as missing values instead of shifting the reading position. This is particularly useful for handling situations where columns might be shorter than expected.
Example:
data mydata;
infile 'your_file.txt' missover;
input
name $10.
age 3.
city $15.;
run;
2. Using `TRUNCOVER` option:
Similar to MISSOVER, TRUNCOVER also helps prevent shifted reads when the input line ends prematurely. It differs slightly in its handling of short records. While MISSOVER will return missing values for fields that are not present due to short record lengths, TRUNCOVER will treat the values as present with whatever data is available till end of the record.
Example:
data mydata;
infile 'your_file.txt' truncover;
input
name $10.
age 3.
city $15.;
run;
3. Using Delimited Files:
If your data is in a delimited format (e.g., CSV, tab-delimited), SAS can be set to read these files more robustly.
Example (for CSV):
data mydata;
infile 'your_file.csv' dsd dlm=',' missover;
input
name $
age
city $;
run;
The DSD option handles multiple delimiters and quoted values correctly while DLM=',' defines the delimiter, ensuring that missing fields are still correctly aligned.
4. Using Column Input with `?` or `??` modifiers:
SAS allows using modifiers like '?' or '??' with column inputs to handle errors. A single '?' suppresses notes about invalid data, and a '??' suppresses error messages completely. This is helpful in managing missing character inputs. It is very beneficial when some of the character columns can have missing or invalid data which you want to treat as missing without throwing errors and notes.
Example:
data mydata;
infile 'your_file.txt';
input
name $10.?
age 3.
city $15.?;
run;
Recommendations:
- Always review your data and understand the data format.
- Use MISSOVER or TRUNCOVER in conjunction with fixed-width data.
- Use delimited formats (e.g., CSV) for greater flexibility.
- Employ ? or ?? error suppression if you know your character data has missing or invalid values.
- Validate the imported data to verify the values are as expected.
By applying these strategies, you can effectively handle missing characters in SAS data files and avoid misaligned input. This will help in producing clean and accurate data sets, regardless of the inconsistencies present in the input data.