How can I selectively merge or pick changes from another branch in Git?

I had the exact same problem as mentioned by you above. But I found this clearer in explaining the answer.

Summary:

• Check out the path(s) from the branch you want to merge,

   $ git checkout source_branch -- <paths>...
  
  Hint: It also works without `--` like seen in the linked post.
  

• or to selectively merge hunks

   $ git checkout -p source_branch -- <paths>...
  

Alternatively, use reset and then add with the option -p,

    $ git reset <paths>...
    $ git add -p <paths>...

• Finally commit

   $ git commit -m "'Merge' these changes"