Length of Subset

[Gabriel Perren]

Hi! I'm looking for a simple way of knowing how many elements are in a given subset. Right now I do one of two things:

# Approach 1

1. Open up the terminal

2. Drag/drop the subset, name it 's1'

3. Type: `s1.to_mask().sum()`

# Approach 2

1. Export the subset to a file

2. Open file and check how many lines there are

Either one is a bit cumbersome when I have to repeat it for many files. I'd like to add a custom button for the viewer toolbar that would show me this information when pressed. Is this possible?

Thank you!