# Filter Grammar Functions

When used without qualification, filter axes (feature, match, region, tag) return lists of items. These lists cannot be tested directly, but they can be supplied to the count() function, the result of which can be tested.

In addition, vectors of string (e.g. sets) can also be supplied to count(), but not to the other functions.

Additionally, when any axis floating point variable is provided using a path separator instead of a part of an axis filter, it will return a list of values which cannot be tested directly, but can be supplied directly to the min() and max() functions, and those results can be tested.

For example:

- count (feature) > 10 // Returns views that have more than ten features.
- min (feature/score) < 0.95 // Returns views where the minimum score for any feature is less than 0.95.
- count (sets) > 1 // Returns views that are members of more than one set.

Operator | Notes
--- | ---
count() |
min() |
max() |
sum() |
avg() |
std() |