Assigning a key to expand or collapse a group

Hi, i would like to have a key assigned to expanding or collapsing a group,
so I don't have to navigate the menu bar to do this. Eg. I often sort my
emails by author. In searching for emails by some one's name, often I will
navigate to the top of the menu, view --> expand collapse groups --> collapse
group, and then navigate down to the name in question.

I would like to assign one key for expanding and another for collapsing the
groups so I don't have to do this manually every time.

Help is much appreciated!!

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