Sometimes you want to choose between two values, based on some condition, before passing the choice to the pipe.
You could use the JavaScript ternary operator (?:) in the template to make that choice.
Beware! The pipe operator has a higher precedence than the JavaScript ternary operator (?:).
If you simply write the expression as if it were evaluated left-to-right, you might be surprised by the result. For example,
condition ? a : b | pipe
is parsed as
condition ? a : (b | pipe)
The value of b passes through pipe; the value of a will not.
If you want the pipe to apply to the result of the ternary expression, wrap the entire expression in parentheses. For example,
(condition ? a : b) | pipe
In general, you should always use parentheses to be sure Angular evaluates the expression as you intend.