Filtering phone numbers that are not from El Salvador means identifying numbers that do not conform to the established El Salvador phone number formats. This is essentially the inverse of validating El Salvador numbers. The most effective way to do this is to define what an El Salvador number looks like and then reject anything that doesn't fit.
Understanding El Salvador Phone Number Characteristics
To filter out non-El Salvador numbers, you first need a clear definition of what is an El Salvador number. Here are the key characteristics:
Country Code: The international dialing code for El Salvador is +503. Any number without this country code (or a clear intention of being a domestic number el-salvador phone number list within El Salvador where the country code is implied) is immediately suspect.
National Significant Number (NSN) Length: Most standard El Salvador phone numbers (both fixed and mobile) have eight digits when the country code is excluded.
Starting Digits for 8-Digit Numbers:
Fixed lines (landlines) typically start with 2, 3, 4, or 5.
Mobile numbers typically start with 6 or 7.
Special Service Numbers (7 or 11 digits): While less common, it's important to consider:
Freephone (Toll-Free): These numbers usually start with 800 and can be 7 or 11 digits long (e.g., 800 XXXX or 800 XXXX XXXX).
Premium Rate: These numbers usually start with 900 and can also be 7 or 11 digits long (e.g., 900 XXXX or 900 XXXX XXXX).
Strategies for Filtering Non-El Salvador Numbers
Here are the primary strategies to filter out numbers not from El Salvador:
Prefix Check (Most Common Method):
The most straightforward approach is to check for the presence and correctness of the international dialing code.
If numbers are expected to be in international format: Look for +503 at the beginning of the number. If a number doesn't start with +503, it's not an El Salvador number in international format.
If numbers are a mix of international and domestic: You'll need a more sophisticated check. First, try to identify numbers that do start with +503. For those that don't, you then need to assume they might be domestic El Salvador numbers and apply the internal formatting rules. Any number that doesn't match either the international or domestic El Salvador formats can then be filtered out.
Regular Expressions (Regex) for Pattern Matching:
This is the most powerful and flexible method. You define a regex pattern that only valid El Salvador numbers should match. Any number that fails to match this pattern is considered not from El Salvador.