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Is this a robust way to distinguish explicitly installed packages from those pulled in as dependencies?

When exploring the commands from [this answer to my previous question,][1] I found that the ist of packages includes a lot that were automatically installed due to dependencies. Obviously I'm interested only in those packages that I explicitly requested (the others would be pulled in automatically again, if needed).

Since I didn't figure out a way to explicitly query whether a package was installed explicitly or as dependency, I figured the best way would be to determine whether a package depends on another installed package.

This information turns out to be available with `apt-cache rdepends --installed $packagename` but I still need to extract the information I need from the output.

Unfortunately the line "Reverse Depends:" is always output, even if there are no reverse dependencies. However I noticed that the dependency lines all start with a space, while the others don't. Therefore my idea is to use the following:
```
apt-cache rdepends --installed $packagename | grep -q "^ "
```
If there are no dependencies, the exit status of grep will be 1, otherwise it will be 0.

My question now is: Is this a robust way to test for this? If not, what are better ways to achieve what I want?


 [1]: https://linux.codidact.com/posts/281848#answer-281850