Filter
Purpose 
Returns from textToFilter only those characters specified in filterText, in the order they were originally entered in textToFilter.
Format 
Filter(textToFilter;filterText)
Parameters 
textToFilter - any text expression or text field
filterText - the characters to preserve in the specified text
Data type returned 
text
Originated in 
FileMaker Pro 7.0
Description 
If filterText doesn’t have any characters, an empty string is returned. The Filter function is case-sensitive.
Examples 
Filter(“(408)555-1212”;“0123456789”) returns 4085551212.
Filter(“AaBb”;“AB”) returns AB.
The following example removes all text from the provided data, then formats the remaining numbers in the preferred phone number formatting:
Let(phone = filter(theField;“0123456789”);“(“ & left(phone;3) & “)” & middle(phone;4;3) & “-” & middle(phone;7;4))
If theField contains Work: 408.555.1212 this calculation returns (408)555-1212.
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas